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Brain Anatomy and How the Brain Works

What is the brain.

The brain is a complex organ that controls thought, memory, emotion, touch, motor skills, vision, breathing, temperature, hunger and every process that regulates our body. Together, the brain and spinal cord that extends from it make up the central nervous system, or CNS.

What is the brain made of?

Weighing about 3 pounds in the average adult, the brain is about 60% fat. The remaining 40% is a combination of water, protein, carbohydrates and salts. The brain itself is a not a muscle. It contains blood vessels and nerves, including neurons and glial cells.

What is the gray matter and white matter?

Gray and white matter are two different regions of the central nervous system. In the brain, gray matter refers to the darker, outer portion, while white matter describes the lighter, inner section underneath. In the spinal cord, this order is reversed: The white matter is on the outside, and the gray matter sits within.

Gray matter is primarily composed of neuron somas (the round central cell bodies), and white matter is mostly made of axons (the long stems that connects neurons together) wrapped in myelin (a protective coating). The different composition of neuron parts is why the two appear as separate shades on certain scans.

Each region serves a different role. Gray matter is primarily responsible for processing and interpreting information, while white matter transmits that information to other parts of the nervous system.

How does the brain work?

The brain sends and receives chemical and electrical signals throughout the body. Different signals control different processes, and your brain interprets each. Some make you feel tired, for example, while others make you feel pain.

Some messages are kept within the brain, while others are relayed through the spine and across the body’s vast network of nerves to distant extremities. To do this, the central nervous system relies on billions of neurons (nerve cells).

Main Parts of the Brain and Their Functions

At a high level, the brain can be divided into the cerebrum, brainstem and cerebellum.

The cerebrum (front of brain) comprises gray matter (the cerebral cortex) and white matter at its center. The largest part of the brain, the cerebrum initiates and coordinates movement and regulates temperature. Other areas of the cerebrum enable speech, judgment, thinking and reasoning, problem-solving, emotions and learning. Other functions relate to vision, hearing, touch and other senses.

Cerebral Cortex

Cortex is Latin for “bark,” and describes the outer gray matter covering of the cerebrum. The cortex has a large surface area due to its folds, and comprises about half of the brain’s weight.

The cerebral cortex is divided into two halves, or hemispheres. It is covered with ridges (gyri) and folds (sulci). The two halves join at a large, deep sulcus (the interhemispheric fissure, AKA the medial longitudinal fissure) that runs from the front of the head to the back. The right hemisphere controls the left side of the body, and the left half controls the right side of the body. The two halves communicate with one another through a large, C-shaped structure of white matter and nerve pathways called the corpus callosum. The corpus callosum is in the center of the cerebrum.

The brainstem (middle of brain) connects the cerebrum with the spinal cord. The brainstem includes the midbrain, the pons and the medulla.

• Midbrain. The midbrain (or mesencephalon) is a very complex structure with a range of different neuron clusters (nuclei and colliculi), neural pathways and other structures. These features facilitate various functions, from hearing and movement to calculating responses and environmental changes. The midbrain also contains the substantia nigra, an area affected by Parkinson’s disease that is rich in dopamine neurons and part of the basal ganglia, which enables movement and coordination.
• Pons. The pons is the origin for four of the 12 cranial nerves, which enable a range of activities such as tear production, chewing, blinking, focusing vision, balance, hearing and facial expression. Named for the Latin word for “bridge,” the pons is the connection between the midbrain and the medulla.
• Medulla. At the bottom of the brainstem, the medulla is where the brain meets the spinal cord. The medulla is essential to survival. Functions of the medulla regulate many bodily activities, including heart rhythm, breathing, blood flow, and oxygen and carbon dioxide levels. The medulla produces reflexive activities such as sneezing, vomiting, coughing and swallowing.

The spinal cord extends from the bottom of the medulla and through a large opening in the bottom of the skull. Supported by the vertebrae, the spinal cord carries messages to and from the brain and the rest of the body.

The cerebellum (“little brain”) is a fist-sized portion of the brain located at the back of the head, below the temporal and occipital lobes and above the brainstem. Like the cerebral cortex, it has two hemispheres. The outer portion contains neurons, and the inner area communicates with the cerebral cortex. Its function is to coordinate voluntary muscle movements and to maintain posture, balance and equilibrium. New studies are exploring the cerebellum’s roles in thought, emotions and social behavior, as well as its possible involvement in addiction, autism and schizophrenia.

Brain Coverings: Meninges

Three layers of protective covering called meninges surround the brain and the spinal cord.

• The outermost layer, the dura mater , is thick and tough. It includes two layers: The periosteal layer of the dura mater lines the inner dome of the skull (cranium) and the meningeal layer is below that. Spaces between the layers allow for the passage of veins and arteries that supply blood flow to the brain.
• The arachnoid mater is a thin, weblike layer of connective tissue that does not contain nerves or blood vessels. Below the arachnoid mater is the cerebrospinal fluid, or CSF. This fluid cushions the entire central nervous system (brain and spinal cord) and continually circulates around these structures to remove impurities.
• The pia mater is a thin membrane that hugs the surface of the brain and follows its contours. The pia mater is rich with veins and arteries.

Lobes of the Brain and What They Control

Each brain hemisphere (parts of the cerebrum) has four sections, called lobes: frontal, parietal, temporal and occipital. Each lobe controls specific functions.

• Frontal lobe. The largest lobe of the brain, located in the front of the head, the frontal lobe is involved in personality characteristics, decision-making and movement. Recognition of smell usually involves parts of the frontal lobe. The frontal lobe contains Broca’s area, which is associated with speech ability.
• Parietal lobe. The middle part of the brain, the parietal lobe helps a person identify objects and understand spatial relationships (where one’s body is compared with objects around the person). The parietal lobe is also involved in interpreting pain and touch in the body. The parietal lobe houses Wernicke’s area, which helps the brain understand spoken language.
• Occipital lobe. The occipital lobe is the back part of the brain that is involved with vision.
• Temporal lobe. The sides of the brain, temporal lobes are involved in short-term memory, speech, musical rhythm and some degree of smell recognition.

Deeper Structures Within the Brain

Pituitary gland.

Sometimes called the “master gland,” the pituitary gland is a pea-sized structure found deep in the brain behind the bridge of the nose. The pituitary gland governs the function of other glands in the body, regulating the flow of hormones from the thyroid, adrenals, ovaries and testicles. It receives chemical signals from the hypothalamus through its stalk and blood supply.

Hypothalamus

The hypothalamus is located above the pituitary gland and sends it chemical messages that control its function. It regulates body temperature, synchronizes sleep patterns, controls hunger and thirst and also plays a role in some aspects of memory and emotion.

Small, almond-shaped structures, an amygdala is located under each half (hemisphere) of the brain. Included in the limbic system, the amygdalae regulate emotion and memory and are associated with the brain’s reward system, stress, and the “fight or flight” response when someone perceives a threat.

Hippocampus

A curved seahorse-shaped organ on the underside of each temporal lobe, the hippocampus is part of a larger structure called the hippocampal formation. It supports memory, learning, navigation and perception of space. It receives information from the cerebral cortex and may play a role in Alzheimer’s disease.

Pineal Gland

The pineal gland is located deep in the brain and attached by a stalk to the top of the third ventricle. The pineal gland responds to light and dark and secretes melatonin, which regulates circadian rhythms and the sleep-wake cycle.

Ventricles and Cerebrospinal Fluid

Deep in the brain are four open areas with passageways between them. They also open into the central spinal canal and the area beneath arachnoid layer of the meninges.

The ventricles manufacture cerebrospinal fluid , or CSF, a watery fluid that circulates in and around the ventricles and the spinal cord, and between the meninges. CSF surrounds and cushions the spinal cord and brain, washes out waste and impurities, and delivers nutrients.

Blood Supply to the Brain

Two sets of blood vessels supply blood and oxygen to the brain: the vertebral arteries and the carotid arteries.

The external carotid arteries extend up the sides of your neck, and are where you can feel your pulse when you touch the area with your fingertips. The internal carotid arteries branch into the skull and circulate blood to the front part of the brain.

The vertebral arteries follow the spinal column into the skull, where they join together at the brainstem and form the basilar artery , which supplies blood to the rear portions of the brain.

The circle of Willis , a loop of blood vessels near the bottom of the brain that connects major arteries, circulates blood from the front of the brain to the back and helps the arterial systems communicate with one another.

Cranial Nerves

Inside the cranium (the dome of the skull), there are 12 nerves, called cranial nerves:

• Cranial nerve 1: The first is the olfactory nerve, which allows for your sense of smell.
• Cranial nerve 2: The optic nerve governs eyesight.
• Cranial nerve 3: The oculomotor nerve controls pupil response and other motions of the eye, and branches out from the area in the brainstem where the midbrain meets the pons.
• Cranial nerve 4: The trochlear nerve controls muscles in the eye. It emerges from the back of the midbrain part of the brainstem.
• Cranial nerve 5: The trigeminal nerve is the largest and most complex of the cranial nerves, with both sensory and motor function. It originates from the pons and conveys sensation from the scalp, teeth, jaw, sinuses, parts of the mouth and face to the brain, allows the function of chewing muscles, and much more.
• Cranial nerve 6: The abducens nerve innervates some of the muscles in the eye.
• Cranial nerve 7: The facial nerve supports face movement, taste, glandular and other functions.
• Cranial nerve 8: The vestibulocochlear nerve facilitates balance and hearing.
• Cranial nerve 9: The glossopharyngeal nerve allows taste, ear and throat movement, and has many more functions.
• Cranial nerve 10: The vagus nerve allows sensation around the ear and the digestive system and controls motor activity in the heart, throat and digestive system.
• Cranial nerve 11: The accessory nerve innervates specific muscles in the head, neck and shoulder.
• Cranial nerve 12: The hypoglossal nerve supplies motor activity to the tongue.

The first two nerves originate in the cerebrum, and the remaining 10 cranial nerves emerge from the brainstem, which has three parts: the midbrain, the pons and the medulla.

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Parts of the Brain: Anatomy, Structure & Functions

Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

Learn about our Editorial Process

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

On This Page:

The brain controls all functions of the body, interprets information from the outside world, and defines who we are as individuals and how we experience the world.

The brain receives information through our senses: sight, touch, taste, smell, and hearing. This information is processed in the brain, allowing us to give meaning to the input it receives.

The brain is part of the central nervous system ( CNS ) along with the spinal cord. There is also a peripheral nervous system (PNS) comprised of 31 pairs of spinal nerves that branch from the spinal cord and cranial nerves that branch from the brain.

Brain Parts

The brain is composed of the cerebrum, cerebellum, and brainstem (Fig. 1).

Figure 1. The brain has three main parts: the cerebrum, cerebellum, and brainstem.

The cerebrum is the largest and most recognizable part of the brain. It consists of grey matter (the cerebral cortex ) and white matter at the center. The cerebrum is divided into two hemispheres, the left and right, and contains the lobes of the brain (frontal, temporal, parietal, and occipital lobes).

The cerebrum produces higher functioning roles such as thinking, learning, memory, language, emotion, movement, and perception.

The Cerebellum

The cerebellum is located under the cerebrum and monitors and regulates motor behaviors, especially automatic movements.

This structure is also important for regulating posture and balance and has recently been suggested for being involved in learning and attention.

Although the cerebellum only accounts for roughly 10% of the brain’s total weight, this area is thought to contain more neurons (nerve cells) than the rest of the brain combined.

The brainstem is located at the base of the brain. This area connects the cerebrum and the cerebellum to the spinal cord, acting as a relay station for these areas.

The brainstem regulates automatic functions such as sleep cycles, breathing, body temperature, digestion, coughing, and sneezing.

Right Brain vs. Left Brain

The cerebrum is divided into two halves: the right and left hemispheres (Fig. 2). The left hemisphere controls the right half of the body, and the right hemisphere controls the left half.

The two hemispheres are connected by a thick band of neural fibers known as the corpus callosum, consisting of about 200 million axons.

The corpus callosum allows the two hemispheres to communicate and allows information being processed on one side of the brain to be shared with the other.

Figure 2. The cerebrum is divided into left and right hemispheres. The nerve fibers corpus callosum connects the two sides.

Hemispheric lateralization is the idea that each hemisphere is responsible for different functions. Each of these functions is localized to either the right or left side.

The left hemisphere is associated with language functions, such as formulating grammar and vocabulary and containing different language centers (Broca’s and Wernicke’s area).

The right hemisphere is associated with more visuospatial functions such as visualization, depth perception, and spatial navigation. These left and right functions are the case in most people, especially those who are right-handed.

Lobes of the Brain

Each cerebral hemisphere can be subdivided into four lobes, each associated with different functions.

The four lobes of the brain are the frontal, parietal, temporal, and occipital lobes (Figure 3).

Figure 3. The cerebrum is divided into four lobes: frontal, parietal, occipital, and temporal.

Frontal lobes

The frontal lobes are located at the front of the brain, behind the forehead (Figure 4).

Their main functions are associated with higher cognitive functions, including problem-solving, decision-making, attention, intelligence, and voluntary behaviors.

The frontal lobes contain the motor cortex  responsible for planning and coordinating movements.

It also contains the prefrontal cortex, which is responsible for initiating higher-lever cognitive functioning, and Broca’s Area, which is essential for language production.

Figure 4. Frontal lobe structure.

Temporal lobes

The temporal lobes are located on both sides of the brain, near the temples of the head, hence the name temporal lobes (Figure 5).

The main functions of these lobes include understanding, language, memory acquisition, face recognition, object recognition, perception, and auditory information processing.

There is a temporal lobe in both the left and right hemispheres. The left temporal lobe, which is usually the most dominant in people, is associated with language, learning, memorizing, forming words, and remembering verbal information.

The left lobe also contains a vital language center known as Wernicke’s area, which is essential for language development. The right temporal lobe is usually associated with learning and memorizing non-verbal information and determining facial expressions.

Figure 5. Temporal lobe structure.

Parietal lobes

The parietal lobe is located at the top of the brain, between the frontal and occipital lobes, and above the temporal lobes (Figure 6).

The parietal lobe is essential for integrating information from the body’s senses to allow us to build a coherent picture of the world around us.

These lobes allow us to perceive our bodies through somatosensory information (e.g., through touch, pressure, and temperature). It can also help with visuospatial processing, reading, and number representations (mathematics).

The parietal lobes also contain the somatosensory cortex, which receives and processes sensory information, integrating this into a representational map of the body.

This means it can pinpoint the exact area of the body where a sensation is felt, as well as perceive the weight of objects, shape, and texture.

Figure 6. Parietal lobe structure.

Occipital lobes

The occipital lobes are located at the back of the brain behind the temporal and parietal lobes and below the occipital bone of the skull (Figure 7).

The occipital lobes receive sensory information from the eyes’ retinas, which is then encoded into different visual data. Some of the functions of the occipital lobes include being able to assess the size, depth, and distance, determine color information, object and facial recognition, and mapping the visual world.

The occipital lobes also contain the primary visual cortex, which receives sensory information from the retinas, transmitting this information relating to location, spatial data, motion, and the colors of objects in the field of vision.

Figure 7. Occipital lobe structure.

Cerebral Cortex

The surface of the cerebrum is called the cerebral cortex  and has a wrinkled appearance, consisting of bulges, also known as gyri, and deep furrows, known as sulci (Figure 8).

A gyrus (plural: gyri) is the name given to the bumps and ridges on the cerebral cortex (the outermost layer of the brain). A sulcus (plural: sulci) is another name for a groove in the cerebral cortex.

Figure 8. The cortex contains neurons (grey matter) interconnected to other brain areas by axons (white matter). The cortex has a folded appearance. A fold is called a gyrus, and the valley between is a sulcus.

The cerebral cortex is primarily constructed of grey matter (neural tissue made up of neurons), with between 14 and 16 billion neurons found here.

The many folds and wrinkles of the cerebral cortex allow a wider surface area for an increased number of neurons to live there, permitting large amounts of information to be processed.

Deep Structures

The amygdala is a structure deep in the brain that is involved in the processing of emotions and fear learning. The amygdala is a part of the limbic system, a neural network that mediates emotion and memory (Figure 9).

This structure also ties emotional meaning to memories, processes rewards, and helps us make decisions. This structure has also been linked with the fight-or-flight response.

Figure 9. The amygdala in the limbic system plays a key role in how animals assess and respond to environmental threats and challenges by evaluating the emotional importance of sensory information and prompting an appropriate response.

Thalamus and Hypothalamus

The thalamus relays information between the cerebral cortex, brain stem, and other cortical structures (Figure 10).

Because of its interactive role in relaying sensory and motor information, the thalamus contributes to many processes, including attention, perception, timing, and movement. The hypothalamus modulates a range of behavioral and physiological functions.

It controls autonomic functions such as hunger, thirst, body temperature, and sexual activity. To do this, the hypothalamus integrates information from different brain parts and responds to various stimuli such as light, odor, and stress.

Figure 10. The thalamus is often described as the brain’s relay station as a great deal of information that reaches the cerebral cortex first stops in the thalamus before being sent to its destination.

Hippocampus

The hippocampus is a curved-shaped structure in the limbic system associated with learning and memory (Figure 11).

This structure is most strongly associated with the formation of memories, is an early storage system for new long-term memories, and plays a role in the transition of these long-term memories to more permanent memories.

Figure 11. Hippocampus location in the brain

Basal Ganglia

The basal ganglia are a group of structures that regulate the coordination of fine motor movements, balance, and posture alongside the cerebellum.

These structures are connected to other motor areas and link the thalamus with the motor cortex. The basal ganglia are also involved in cognitive and emotional behaviors, as well as playing a role in reward and addiction.

Figure 12. The Basal Ganglia Illustration

Ventricles and Cerebrospinal Fluid

Within the brain, there are fluid-filled interconnected cavities called ventricles , which are extensions of the spinal cord. These are filled with a substance called cerebrospinal fluid, which is a clear and colorless liquid.

The ventricles produce cerebrospinal fluid and transport and remove this fluid. The ventricles do not have a unique function, but they provide cushioning to the brain and are useful for determining the locations of other brain structures.

Cerebrospinal fluid circulates the brain and spinal cord and functions to cushion the brain within the skull. If damage occurs to the skull, the cerebrospinal fluid will act as a shock absorber to help protect the brain from injury.

As well as providing cushioning, the cerebrospinal fluid circulates nutrients and chemicals filtered from the blood and removes waste products from the brain. Cerebrospinal fluid is constantly absorbed and replenished by the ventricles.

If there were a disruption or blockage, this can cause a build-up of cerebrospinal fluid and can cause enlarged ventricles.

Neurons are the nerve cells of the central nervous system that transmit information through electrochemical signals throughout the body. Neurons contain a soma, a cell body from which the axon extends.

Axons are nerve fibers that are the longest part of the neuron, which conduct electrical impulses away from the soma.

There are dendrites at the end of the neuron, which are branch-like structures that send and receive information from other neurons.

A myelin sheath, a fatty insulating layer, forms around the axon, allowing nerve impulses to travel down the axon quickly.

There are different types of neurons. Sensory neurons transmit sensory information, motor neurons transmit motor information, and relay neurons allow sensory and motor neurons to communicate.

The communication between neurons is called synapses. Neurons communicate with each other via synaptic clefts, which are gaps between the endings of neurons.

During synaptic transmission, chemicals, such as neurotransmitters, are released from the endings of the previous neuron (also known as the presynaptic neuron).

These chemicals enter the synaptic cleft to then be transported to receptors on the next neuron (also known as the postsynaptic neuron).

Once transported to the next neuron, the chemical messengers continue traveling down neurons to influence many functions, such as behavior and movement.

Glial Cells

Glial cells are non-neuronal cells in the central nervous system which work to provide the neurons with nourishment, support, and protection.

These are star-shaped cells that function to maintain the environment for neuronal signaling by controlling the levels of neurotransmitters surrounding the synapses.

They also work to clean up what is left behind after synaptic transmission, either recycling any leftover neurotransmitters or cleaning up when a neuron dies.

Oligodendrocytes

These types of glial have the appearance of balls with spikes all around them. They function by wrapping around the axons of neurons to form a protective layer called the myelin sheath.

This is a substance that is rich in fat and provides insulation to the neurons to aid neuronal signaling.

Microglial cells have oval bodies and many branches projecting out of them. The primary function of these cells is to respond to injuries or diseases in the central nervous system.

They respond by clearing away any dead cells or removing any harmful toxins or pathogens that may be present, so they are, therefore, important to the brain’s health.

Ependymal cells

These cells are column-shaped and usually line up together to form a membrane called the ependyma. The ependyma is a thin membrane lining the spinal cord and ventricles of the brain .

In the ventricles, these cells have small hairlike structures called cilia, which help encourage the flow of cerebrospinal fluid.

Cranial Nerves

There are 12 types of cranial nerves which are linked directly to the brain without having to pass through the spinal cord. These allow sensory information to pass from the organs of the face to the brain:

Mnemonic for Order of Cranial Nerves:

S ome S ay M arry M oney B ut M y B rother S ays B ig B rains M atter M ore

• Cranial I: Sensory
• Cranial II: Sensory
• Cranial III: Motor
• Cranial IV: Motor
• Cranial V: Both (sensory & motor)
• Cranial VI: Motor
• Cranial VII: Both (sensory & motor)
• Cranial VIII: Sensory
• Cranial IX: Both (sensory & motor)
• Cranial X: Both (sensory & motor)
• Cranial XI: Motor
• Cranial XII: Motor

Purves, D., Augustine, G., Fitzpatrick, D., Katz, L., LaMantia, A., McNamara, J., & Williams, S. (2001). Neuroscience 2nd edition . sunderland (ma) sinauer associates. Types of Eye Movements and Their Functions.

Mayfield Brain and Spine (n.d.). Anatomy of the Brain. Retrieved July 28, 2021, from: https://mayfieldclinic.com/pe-anatbrain.htm

Robertson, S. (2018, August 23). What is Grey Matter? News Medical Life Sciences. https://www.news-medical.net/health/What-is-Grey-Matter.aspx

Guy-Evans, O. (2021, April 13). Temporal lobe: definition, functions, and location. Simply Psychology. www.www.www.www.www.www.simplypsychology.org/temporal-lobe.html

Guy-Evans, O. (2021, April 15). Parietal lobe: definition, functions, and location. Simply Psychology. www.www.www.www.www.www.simplypsychology.org/parietal-lobe.html

Guy-Evans, O. (2021, April 19). Occipital lobe: definition, functions, and location. Simply Psychology. www.www.www.www.www.www.simplypsychology.org/occipital-lobe.html

Guy-Evans, O. (2021, May 08). Frontal lobe function, location in brain, damage, more. Simply Psychology. www.www.www.www.www.www.simplypsychology.org/frontal-lobe.html

Guy-Evans, O. (2021, June 09). Gyri and sulci of the brain. Simply Psychology. www.www.www.www.www.www.simplypsychology.org/gyri-and-sulci-of-the-brain.html

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Parts of the Brain and Their Functions

The human brain is the epicenter of our nervous system and plays a pivotal role in virtually every aspect of our lives. It’s a complex, highly organized organ responsible for thoughts, feelings, actions, and interactions with the world around us. Here is a look at the intricate anatomy of the brain, its functions, and the consequences of damage to different areas.

Introduction to the Brain and Its Functions

The brain is an organ of soft nervous tissue that is protected within the skull of vertebrates. It functions as the coordinating center of sensation and intellectual and nervous activity. The brain consists of billions of neurons (nerve cells) that communicate through intricate networks. The primary functions of the brain include processing sensory information, regulating bodily functions, forming thoughts and emotions, and storing memories.

Main Parts of the Brain – Anatomy

The three main parts of the brain are the cerebrum, cerebellum, and brainstem.

1. Cerebrum

• Location: The cerebellum occupies the upper part of the cranial cavity and is the largest part of the human brain.
• Functions: It’s responsible for higher brain functions, including thought, action, emotion, and interpretation of sensory data.
• Effects of Damage: Depending on the area affected, damage leads to memory loss, impaired cognitive skills, changes in personality, and loss of motor control.

2. Cerebellum

• Location: The cerebellum is at the back of the brain, below the cerebrum.
• Functions: It coordinates voluntary movements such as posture, balance, coordination, and speech.
• Effects of Damage: Damage causes problems with balance, movement, and muscle coordination (ataxia).

3. Brainstem

• Location: The brainstem is lower extension of the brain, connecting to the spinal cord. It includes the midbrain, pons, and medulla oblongata.
• Functions: This part of the brain controls many basic life-sustaining functions, including heart rate, breathing, sleeping, and eating.
• Effects of Damage: Damage results in life-threatening conditions like breathing difficulties, heart problems, and loss of consciousness.

Lobes of the Brain

The four lobes of the brain are regions of the cerebrum:

• Location: This is the anterior or front part of the brain.
• Functions: Decision making, problem solving, control of purposeful behaviors, consciousness, and emotions.
• Location: Sits behind the frontal lobe.
• Functions: Processes sensory information it receives from the outside world, mainly relating to spatial sense and navigation (proprioception).
• Location: Below the lateral fissure, on both cerebral hemispheres.
• Functions: Mainly revolves around auditory perception and is also important for the processing of both speech and vision (reading).
• Location: At the back of the brain.
• Functions: Main center for visual processing.

Left vs. Right Brain Hemispheres

The cerebrum has two halves, called hemispheres. Each half controls functions on the opposite side of the body. So, the left hemisphere controls muscles on the right side of the body, and vice versa. But, the functions of the two hemispheres are not entirely identical:

• Left Hemisphere: It’s dominant in language and speech and plays roles in logical thinking, analysis, and accuracy. .
• Right Hemisphere: This hemisphere is more visual and intuitive and functions in creative and imaginative tasks.

The corpus callosum is a band of nerves that connect the two hemispheres and allow communication between them.

Detailed List of Parts of the Brain

While knowing the three key parts of the brain is a good start, the anatomy is quite a bit more complex. In addition to nervous tissues, the brain also contains key glands:

• Cerebrum: The cerebrum is the largest part of the brain. Divided into lobes, it coordinates thought, movement, memory, senses, speech, and temperature.
• Corpus Callosum : A broad band of nerve fibers joining the two hemispheres of the brain, facilitating interhemispheric communication.
• Cerebellum : Coordinates movement and balance and aids in eye movement.
• Pons : Controls voluntary actions, including swallowing, bladder function, facial expression, posture, and sleep.
• Medulla oblongata : Regulates involuntary actions, including breathing, heart rhythm, as well as oxygen and carbon dioxide levels.
• Limbic System : Includes the amygdala, hippocampus, and parts of the thalamus and hypothalamus.
• Amygdala: Plays a key role in emotional responses, hormonal secretions, and memory formation.
• Hippocampus: Plays a vital role in memory formation and spatial navigation.
• Thalamus : Acts as the brain’s relay station, channeling sensory and motor signals to the cerebral cortex, and regulating consciousness, sleep, and alertness.
• Basal Ganglia : A group of structures involved in processing information related to movement, emotions, and reward. Key structures include the striatum, globus pallidus, substantia nigra, and subthalamic nucleus.
• Ventral Tegmental Area (VTA) : Plays a role in the reward circuit of the brain, releasing dopamine in response to stimuli indicating a reward.
• Optic tectum : Also known as the superior colliculus, it directs eye movements.
• Substantia Nigra : Involved in motor control and contains a large concentration of dopamine-producing neurons.
• Cingulate Gyrus : Plays a role in processing emotions and behavior regulation. It also helps regulate autonomic motor function.
• Olfactory Bulb : Involved in the sense of smell and the integration of olfactory information.
• Mammillary Bodies : Plays a role in recollective memory.
• Function: Regulates emotions, memory, and arousal.

Glands in the Brain

The hypothalamus, pineal gland, and pituitary gland are the three endocrine glands within the brain:

• Hypothalamus : The hypothalamus links the nervous and endocrine systems. It contains many small nuclei. In addition to participating in eating and drinking, sleeping and waking, it regulates the endocrine system via the pituitary gland. It maintains the body’s homeostasis, regulating hunger, thirst, response to pain, levels of pleasure, sexual satisfaction, anger, and aggressive behavior.
• Pituitary Gland : Known as the “master gland,” it controls various other hormone glands in the body, such as the thyroid and adrenals, as well as regulating growth, metabolism, and reproductive processes.
• Pineal Gland : The pineal gland produces and regulates some hormones, including melatonin, which is crucial in regulating sleep patterns and circadian rhythms.

Gray Matter vs. White Matter

The brain and spinal cord consist of gray matter (substantia grisea) and white matter (substantia alba).

• White Matter: Consists mainly of axons and myelin sheaths that send signals between different brain regions and between the brain and spinal cord.
• Gray Matter: Consists of neuronal cell bodies, dendrites, and axon terminals. Gray matter processes information and directs stimuli for muscle control, sensory perception, decision making, and self-control.

Frequently Asked Questions (FAQs) About the Human Brain

• The human brain contains approximately 86 billion neurons. Additionally, it has a similar or slightly higher number of non-neuronal cells (glial cells), making the total number of cells in the brain close to 170 billion.
• There are about 86 billion neurons in the human brain. These neurons are connected by trillions of synapses, forming a complex networks.
• The average adult human brain weighs about 1.3 to 1.4 kilograms (about 3 pounds). This weight represents about 2% of the total body weight.
• The brain is about 73% water.
• The myth that humans only use 10% of their brain is false. Virtually every part gets use, and most of the brain is active all the time, even during sleep.
• The average size of the adult human brain is about 15 centimeters (6 inches) in length, 14 centimeters (5.5 inches) in width, and 9 centimeters (3.5 inches) in height.
• Brain signal speeds vary depending on the type of neuron and the nature of the signal. They travel anywhere from 1 meter per second to over 100 meters per second in the fastest neurons.
• With age, the brain’s volume and/or weight decrease, synaptic connections reduce, and there can be a decline in cognitive functions. However, the brain to continues adapting and forming new connections throughout life.
• The brain has a limited ability to repair itself. Neuroplasticity aids recovery by allowing other parts of the brain to take over functions of the damaged areas.
• The brain consumes about 20% of the body’s total energy , despite only making up about 2% of the body’s total weight . It requires a constant supply of glucose and oxygen.
• Sleep is crucial for brain health. It aids in memory consolidation, learning, brain detoxification, and the regulation of mood and cognitive functions.
• Douglas Fields, R. (2008). “White Matter Matters”. Scientific American . 298 (3): 54–61. doi: 10.1038/scientificamerican0308-54
• Kandel, Eric R.; Schwartz, James Harris; Jessell, Thomas M. (2000). Principles of Neural Science (4th ed.). New York: McGraw-Hill. ISBN 978-0-8385-7701-1.
• Kolb, B.; Whishaw, I.Q. (2003). Fundamentals of Human Neuropsychology (5th ed.). New York: Worth Publishing. ISBN 978-0-7167-5300-1.
• Rajmohan, V.; Mohandas, E. (2007). “The limbic system”. Indian Journal of Psychiatry . 49 (2): 132–139. doi: 10.4103/0019-5545.33264
• Shepherd, G.M. (1994). Neurobiology . Oxford University Press. ISBN 978-0-19-508843-4.

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Introduction: The Human Brain

By Helen Phillips

4 September 2006

A false-colour Magnetic Resonance Image (MRI) of a mid-sagittal section through the head of a normal 42 year-old woman, showing structures of the brain, spine and facial tissues

(Image: Mehau Kulyk / Science Photo Library)

The brain is the most complex organ in the human body. It produces our every thought, action , memory , feeling and experience of the world. This jelly-like mass of tissue, weighing in at around 1.4 kilograms, contains a staggering one hundred billion nerve cells, or neurons .

The complexity of the connectivity between these cells is mind-boggling. Each neuron can make contact with thousands or even tens of thousands of others, via tiny structures called synapses . Our brains form a million new connections for every second of our lives. The pattern and strength of the connections is constantly changing and no two brains are alike.

It is in these changing connections that memories are stored, habits learned and personalities shaped , by reinforcing certain patterns of brain activity, and losing others.

Grey matter

While people often speak of their “ grey matter “, the brain also contains white matter . The grey matter is the cell bodies of the neurons, while the white matter is the branching network of thread-like tendrils – called dendrites and axons – that spread out from the cell bodies to connect to other neurons.

But the brain also has another, even more numerous type of cell, called glial cells . These outnumber neurons ten times over. Once thought to be support cells, they are now known to amplify neural signals and to be as important as neurons in mental calculations. There are many different types of neuron, only one of which is unique to humans and the other great apes, the so called spindle cells .

Brain structure is shaped partly by genes , but largely by experience . Only relatively recently it was discovered that new brain cells are being born throughout our lives – a process called neurogenesis . The brain has bursts of growth and then periods of consolidation , when excess connections are pruned. The most notable bursts are in the first two or three years of life, during puberty , and also a final burst in young adulthood.

How a brain ages also depends on genes and lifestyle too. Exercising the brain and giving it the right diet can be just as important as it is for the rest of the body.

Chemical messengers

The neurons in our brains communicate in a variety of ways. Signals pass between them by the release and capture of neurotransmitter and neuromodulator chemicals, such as glutamate , dopamine , acetylcholine , noradrenalin , serotonin and endorphins .

Some neurochemicals work in the synapse , passing specific messages from release sites to collection sites, called receptors. Others also spread their influence more widely, like a radio signal , making whole brain regions more or less sensitive.

These neurochemicals are so important that deficiencies in them are linked to certain diseases. For example, a loss of dopamine in the basal ganglia, which control movements, leads to Parkinson’s disease . It can also increase susceptibility to addiction because it mediates our sensations of reward and pleasure.

Similarly, a deficiency in serotonin , used by regions involved in emotion, can be linked to depression or mood disorders, and the loss of acetylcholine in the cerebral cortex is characteristic of Alzheimer’s disease .

Brain scanning

Within individual neurons, signals are formed by electrochemical pulses. Collectively, this electrical activity can be detected outside the scalp by an electroencephalogram (EEG).

These signals have wave-like patterns , which scientists classify from alpha (common while we are relaxing or sleeping ), through to gamma (active thought). When this activity goes awry, it is called a seizure . Some researchers think that synchronising the activity in different brain regions is important in perception .

Other ways of imaging brain activity are indirect. Functional magnetic resonance imaging ( fMRI ) or positron emission tomography ( PET ) monitor blood flow. MRI scans, computed tomography ( CT ) scans and diffusion tensor images (DTI) use the magnetic signatures of different tissues, X-ray absorption, or the movement of water molecules in those tissues, to image the brain.

These scanning techniques have revealed which parts of the brain are associated with which functions . Examples include activity related to sensations , movement, libido , choices , regrets , motivations and even racism . However, some experts argue that we put too much trust in these results and that they raise privacy issues .

Before scanning techniques were common, researchers relied on patients with brain damage caused by strokes , head injuries or illnesses, to determine which brain areas are required for certain functions . This approach exposed the regions connected to emotions , dreams , memory , language and perception and to even more enigmatic events, such as religious or “ paranormal ” experiences.

One famous example was the case of Phineas Gage , a 19 th century railroad worker who lost part of the front of his brain when a 1-metre-long iron pole was blasted through his head during an explosion. He recovered physically, but was left with permanent changes to his personality , showing for the first time that specific brain regions are linked to different processes.

Structure in mind

The most obvious anatomical feature of our brains is the undulating surfac of the cerebrum – the deep clefts are known as sulci and its folds are gyri. The cerebrum is the largest part of our brain and is largely made up of the two cerebral hemispheres . It is the most evolutionarily recent brain structure, dealing with more complex cognitive brain activities.

It is often said that the right hemisphere is more creative and emotional and the left deals with logic, but the reality is more complex . Nonetheless, the sides do have some specialisations , with the left dealing with speech and language , the right with spatial and body awareness.

See our Interactive Graphic for more on brain structure

Further anatomical divisions of the cerebral hemispheres are the occipital lobe at the back, devoted to vision , and the parietal lobe above that, dealing with movement , position, orientation and calculation .

Behind the ears and temples lie the temporal lobes , dealing with sound and speech comprehension and some aspects of memory . And to the fore are the frontal and prefrontal lobes , often considered the most highly developed and most “human” of regions, dealing with the most complex thought, decision making , planning, conceptualising, attention control and working memory. They also deal with complex social emotions such as regret , morality and empathy .

Another way to classify the regions is as sensory cortex and motor cortex , controlling incoming information, and outgoing behaviour respectively.

Below the cerebral hemispheres, but still referred to as part of the forebrain, is the cingulate cortex , which deals with directing behaviour and pain . And beneath this lies the corpus callosum , which connects the two sides of the brain. Other important areas of the forebrain are the basal ganglia , responsible for movement , motivation and reward.

Urges and appetites

Beneath the forebrain lie more primitive brain regions. The limbic system , common to all mammals, deals with urges and appetites. Emotions are most closely linked with structures called the amygdala , caudate nucleus and putamen . Also in the limbic brain are the hippocampus – vital for forming new memories; the thalamus – a kind of sensory relay station; and the hypothalamus , which regulates bodily functions via hormone release from the pituitary gland .

The back of the brain has a highly convoluted and folded swelling called the cerebellum , which stores patterns of movement, habits and repeated tasks – things we can do without thinking about them.

The most primitive parts, the midbrain and brain stem , control the bodily functions we have no conscious control of, such as breathing , heart rate, blood pressure, sleep patterns , and so on. They also control signals that pass between the brain and the rest of the body, through the spinal cord.

Though we have discovered an enormous amount about the brain, huge and crucial mysteries remain. One of the most important is how does the brain produces our conscious experiences ?

The vast majority of the brain’s activity is subconscious . But our conscious thoughts, sensations and perceptions – what define us as humans – cannot yet be explained in terms of brain activity.

• psychology /

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The human brain, explained

Learn about the most complex organ in the human body, from its structure to its most common disorders.

Here’s something to wrap your mind around: The human brain is more complex than any other known structure in the universe . Weighing in at three pounds, on average, this spongy mass of fat and protein is made up of two overarching types of cells—called glia and neurons—and it contains many billions of each. Neurons are notable for their branch-like projections called axons and dendrites, which gather and transmit electrochemical signals. Different types of glial cells provide physical protection to neurons and help keep them, and the brain, healthy.

Together, this complex network of cells gives rise to every aspect of our shared humanity. We could not breathe, play, love, or remember without the brain.

Anatomy of the brain

The cerebrum is the largest part of the brain , accounting for 85 percent of the organ's weight. The distinctive, deeply wrinkled outer surface is the cerebral cortex. It's the cerebrum that makes the human brain—and therefore humans—so formidable. Animals such as elephants, dolphins, and whales actually have larger brains, but humans have the most developed cerebrum. It's packed to capacity inside our skulls, with deep folds that cleverly maximize the total surface area of the cortex .

The cerebrum has two halves, or hemispheres, that are further divided into four regions, or lobes. The frontal lobes, located behind the forehead, are involved with speech, thought, learning, emotion, and movement. Behind them are the parietal lobes, which process sensory information such as touch, temperature, and pain. At the rear of the brain are the occipital lobes, dealing with vision. Lastly, there are the temporal lobes, near the temples, which are involved with hearing and memory.

The second-largest part of the brain is the cerebellum , which sits beneath the back of the cerebrum. It plays an important role in coordinating movement, posture, and balance.

The third-largest part is the diencephalon, located in the core of the brain. A complex of structures roughly the size of an apricot, its two major sections are the thalamus and hypothalamus. The thalamus acts as a relay station for incoming nerve impulses from around the body that are then forwarded to the appropriate brain region for processing. The hypothalamus controls hormone secretions from the nearby pituitary gland. These hormones govern growth and instinctual behaviors, such as when a new mother starts to lactate. The hypothalamus is also important for keeping bodily processes like temperature, hunger, and thirst balanced.

For Hungry Minds

Seated at the organ's base, the brain stem controls reflexes and basic life functions such as heart rate, breathing, and blood pressure. It also regulates when you feel sleepy or awake and connects the cerebrum and cerebellum to the spinal cord.

The brain is extremely sensitive and delicate, and so it requires maximum protection, which is provided by the hard bone of the skull and three tough membranes called meninges. The spaces between these membranes are filled with fluid that cushions the brain and keeps it from being damaged by contact with the inside of the skull.

Blood-brain barrier

Want more proof that the brain is extraordinary? Look no further than the blood-brain barrier. The discovery of this unique feature dates to the 19th century, when various experiments revealed that dye, when injected into the bloodstream, colored all of the body’s organs except the brain and spinal cord. The same dye, when injected into the spinal fluid, tinted only the brain and spinal cord.

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This led scientists to learn that the brain has an ingenious, protective layer. Called the blood-brain barrier, it’s made up of special, tightly bound cells that together function as a kind of semi-permeable gate throughout most of the organ . It keeps the brain environment safe and stable by preventing some toxins, pathogens, and other harmful substances from entering the brain through the bloodstream, while simultaneously allowing oxygen and vital nutrients to pass through.

Health conditions of the brain

Of course, when a machine as finely calibrated and complex as the brain gets injured or malfunctions, problems arise. One in five Americans suffers from some form of neurological damage , a wide-ranging list that includes stroke, epilepsy, and cerebral palsy, as well as dementia.

Alzheimer’s disease , which is characterized in part by a gradual progression of short-term memory loss, disorientation, and mood swings, is the most common cause of dementia . It is the sixth leading cause of death in the United States, and the number of people diagnosed with it is growing. Worldwide, some 50 million people suffer from Alzheimer’s or some form of dementia. While there are a handful of drugs available to mitigate Alzheimer’s symptoms, there is no cure. Researchers across the globe continue to develop treatments that one day might put an end to the disease’s devasting effects.

Far more common than neurological disorders, however, are conditions that fall under a broad category called mental illness . Unfortunately, negative attitudes toward people who suffer from mental illness are widespread. The stigma attached to mental illness can create feelings of shame, embarrassment, and rejection, causing many people to suffer in silence. In the United States, where anxiety disorders are the most common forms of mental illness, only about 40 percent of sufferers receive treatment. Anxiety disorders often stem from abnormalities in the brain’s hippocampus and prefrontal cortex.

Attention-deficit/hyperactivity disorder, or ADHD , is a mental health condition that also affects adults but is far more often diagnosed in children. ADHD is characterized by hyperactivity and an inability to stay focused. While the exact cause of ADHD has not yet been determined, scientists believe that it may be linked to several factors, among them genetics or brain injury. Treatment for ADHD may include psychotherapy as well as medications. The latter can help by increasing the brain chemicals dopamine and norepinephrine, which are vital to thinking and focusing.

Depression is another common mental health condition. It is the leading cause of disability worldwide and is often accompanied by anxiety. Depression can be marked by an array of symptoms, including persistent sadness, irritability, and changes in appetite. The good news is that in general, anxiety and depression are highly treatable through various medications—which help the brain use certain chemicals more efficiently—and through forms of therapy.

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Physiology, brain.

Kenia A. Maldonado ; Khalid Alsayouri .

Affiliations

Last Update: March 17, 2023 .

• Introduction

The human brain is perhaps the most complex of all biological systems, with the mature brain composed of more than 100 billion information-processing cells called neurons. [1]  The brain is an organ composed of nervous tissue that commands task-evoked responses, movement, senses, emotions, language, communication, thinking, and memory. The three main parts of the human brain are the cerebrum, cerebellum, and brainstem. 

The cerebrum is divided into the right and left hemispheres and is the largest part of the brain. It contains folds and convolutions on its surface, with the ridges found between the convolutions called gyri and the valleys between the gyri called sulci (plural of sulcus). If the sulci are deep, they are called fissures. Both cerebral hemispheres have an outer layer of gray matter called the cerebral cortex and inner subcortical white matter.

Located in the posterior cranial fossa, above the foramen magnum, the cerebellum's primary function is to modulate motor coordination, posture, and balance. It is comprised of the cerebellar cortex and deep cerebellar nuclei, with the cerebellar cortex being made up of three layers; the molecular, Purkinje, and granular layers. The cerebellum connects to the brainstem via cerebellar peduncles.

The brainstem contains the midbrain, pons, and medulla. It is located anterior to the cerebellum, between the base of the cerebrum and the spinal cord.

• Issues of Concern

Studies of brain function have focused on analyzing the variations of the electrical activity produced by the application of sensory stimuli. However, it is also essential to study additional features and functions of the brain, including information processing and responding to environmental demands. [2]

The brain works precisely, making connections, and is a deeply divided structure that has remained not entirely explained or examined. [3]  Although researchers have made significant progress in experimental techniques, the human cognitive function that emerges from neuronal structure and dynamics is not entirely understood. [4]

• Cellular Level

At the beginning of the forebrain formation, the neuroepithelial cells undergo divisions at the inner surface of the neural tube to generate new progenitors. These dividing neuroepithelial cells transform and diversify, leading to radial glial cells (RGCs).

RGCs also work as progenitors with the capacity to regenerate themselves and produce other types of progenitors, neurons, and glial cells. [5]  RGCs have long processes that connect with the neuroepithelium and function as a guide for the migration of neuron cells to ensure that neurons find their resting place, mature, and send out axons and dendrites to participate directly in synapses and electrical signaling. Neurons get produced along with glial cells; glial cells bring support and create an enclosed environment in which neurons can perform their functions.

Glial cells (astrocytes, oligodendrocytes, microglial cells) have well-known roles, which include: keeping the ionic medium of neurons, controlling the rate of nerve signal propagation and synaptic action by regulating the uptake of neurotransmitters, providing a platform for some aspects of neural development, and aiding in recovery from neural damage.

Gray matter is the main component of the central nervous system (CNS) and consists of neuronal cell bodies, dendrites, myelinated and unmyelinated axons, glial cells, synapses, and capillaries. The cerebral cortex is made up of layers of neurons that constitute the gray matter of the brain. The subcortical (beneath the cortex) area is primarily white matter composed of myelinated axons with fewer quantities of cell bodies when compared to gray matter.

Although neurons can have different morphologies, they all contain four common regions: the cell body, the dendrites, the axon, and the axon terminals, each with its respective functions.

The cell body contains a nucleus where proteins and membranes are synthesized. These proteins travel through microtubules down to the axons and terminals via a mechanism known as anterograde transport. In retrograde transport, damaged membranes and organelles travel from the axon toward the cell body along axonal microtubules. Lysosomes are only present in the cell body and are responsible for containing and degrading damaged material. The axon is a thin continuation of a neuron that allows electrical impulses to be sent from neuron to neuron.

Astrocytes occupy 25% of the total brain volume and are the most abundant glial cells. [6]  They are classified into two main groups: protoplasmic and fibrous. Protoplasmic astrocytes appear in gray matter and have several branches that contact both synapses and blood vessels. Fibrous astrocytes are present in the white matter and have long fiber-like processes that contact the nodes of Ranvier and the blood vessels. Astrocytes use their connections to vessels to titrate blood flow in synaptic activity responses. Astrocytic endfeet, which forms tight junctions between endothelial cells and the basal lamina, gives rise to the formation of the blood-brain barrier (BBB). [7]

The primary function of oligodendrocytes is to make myelin, a proteolipid critical in maintaining electrical impulse conduction and maximizing velocity. Myelin is located in segments separated by nodes of Ranvier, and their function is equivalent to those of Schwan cells in the peripheral nervous system.

The macrophage populations of the CNS include microglia, perivascular macrophages, meningeal macrophages, macrophages of the circumventricular organs (CVO), and the microglia of the choroid plexus. Microglia are phagocytic cells representing the immune and support system of the CNS and are the most abundant cells of the choroid plexus. [8]

• Development

Human brain development starts with the neurulation process from the ectodermic layer of the embryo and takes, on average, 20 to 25 years to mature. [9]  It occurs in a sequential and organized manner beginning with the neural tube formation at the third or fourth week of gestation. This is followed by cell migration and proliferation that leads to the folding of the cerebral cortex to increase its size and surface area, creating a more complex structure. Failure of this migration and proliferation leads to a smooth brain without sulci or gyri, termed lissencephaly. [10] At birth, the general architecture of the brain is mostly complete, and by the age of 5 years, the total brain volume is about 95% of its adult size. Generally, the white matter increases with age, while the gray matter decreases with age.

The most prominent white matter structure of the brain, the corpus callosum, increases by approximately 1.8% per year between the ages of 3 and 18 years. [11]  The corpus callosum conjugates the activity of the right and left hemispheres and allows for the progress of higher-order cognitive abilities.

Gray matter in the frontal lobe undergoes continued structural development reaching its maximal volume at 11 to 12 years of age before slowing down during adolescence and early adulthood. The gray matter in the temporal lobe follows a similar development pattern, reaching its maximum size at 16 to 17 years of age with a slight decline afterward. [12]

Below is a list of the brain vesicles and the areas of the brain which develop from them. [13]

Prosencephalon (Forebrain)

• Cerebral cortex
• Basal ganglia (caudate nucleus, putamen, and globus pallidus)
• Hippocampus
• Lateral ventricles
• Hypothalamus
• Epithalamus (pineal gland)
• Subthalamus
• Posterior pituitary
• Optic nerve
• Third ventricle

Mesencephalon (midbrain)

• Cerebral aqueduct

Rhombencephalon (hindbrain)

• Fourth ventricle (rostral)
• Fourth ventricle (caudal)
• Organ Systems Involved

The brain and the spinal cord comprise the central nervous system (CNS). The peripheral nervous system (PNS) subdivides into the somatic nervous system (SNS) and the autonomic nervous system (ANS). The SNS consists of peripheral nerve fibers that collect sensory information to the CNS and motor fibers that send information from the CNS to skeletal muscle. The ANS functions to control the smooth muscle of the viscera and glands and consists of the sympathetic nervous system (SNS), the parasympathetic nervous system (PaNS), and the enteric nervous system (ENS).

Nerves from the brain connect with multiple parts of the head and body, leading to various voluntary and involuntary functions. The ANS drives basic functions that control unconscious activities such as breathing, digestion, sweating, and trembling.

The ENS provides the intrinsic innervation of the gastrointestinal system and is the most neurochemically diverse branch of the PNS. [14]  Neurotransmitters such as norepinephrine, epinephrine, dopamine, and serotonin have recently been a topic of interest due to their roles in gut physiology and CNS pathophysiology, as they aid in regulating gut blood flow, motility, and absorption. [15]

The cerebrum controls motor and sensory information, conscious and unconscious behaviors, feelings, intelligence, and memory. The left hemisphere controls speech and abstract thinking (the ability to think about things that are not present). In contrast, the right hemisphere controls spatial thinking (thinking that finds meaning in the shape, size, orientation, location, and phenomena).

The motor and sensory neurons descending from the brain cross to the opposite side in the brainstem. This crossing means that the right side of the brain controls the motor and sensory functions of the left side of the body, and the left side of the brain controls the motor and sensory functions of the right side of the body. Hence, a stroke affecting the left brain hemisphere, for example, will exhibit motor and sensory deficits on the right side of the body.

Sensory neurons bring sensory input from the body to the thalamus, which then relays this sensory information to the cerebrum. For example, hunger, thirst, and sleep are under the control of the hypothalamus.

The cerebrum is composed of four lobes:

• Frontal lobe: Responsible for motor function, language, and cognitive processes, such as executive function, attention, memory, affect, mood, personality, self-awareness, and social and moral reasoning. [16]  The Broca area is located in the left frontal lobe and is responsible for the production and articulation of speech.
• Parietal lobe: Responsible for interpreting vision, hearing, motor, sensory, and memory functions. 
• Temporal lobe: In the left temporal lobe, the Wernicke area is responsible for understanding spoken and written language. The temporal lobe is also an essential part of the social brain, as it processes sensory information to retain memories, language, and emotions. [17]  The temporal lobe also plays a significant role in hearing and spatial and visual perception.
• Occipital lobe: The visual cortex is located in the occipital lobe and is responsible for interpreting visual information.

The cerebellum controls the coordination of voluntary movement and receives sensory information from the brain and spinal cord to fine-tune the precision and accuracy of motor activity. The cerebellum also aids in various cognitive functions such as attention, language, pleasure response, and fear memory. [18]

The brainstem acts as a bridge that connects the cerebrum and cerebellum to the spinal cord. The brainstem houses the principal centers which perform autonomic functions such as breathing, temperature regulation, respiration, heart rate, wake-sleep cycles, coughing, sneezing, digestion, vomiting, and swallowing. The brainstem contains both white and gray matter. The white matter consists of fiber tracts (neuronal cell axons) traveling down from the cerebral cortex for voluntary motor function and up from the spinal cord and peripheral nerves, allowing somatosensory information to travel to the highest parts of the brain. [19]

The brain represents 2% of the human body weight and consumes 15% of the cardiac output and 20% of total body oxygen. The resting brain consumes 20% of the body's energy supply. When the brain performs a task, the energy consumption increases by an additional 5%, proving that most of the brain's energy consumption gets used for intrinsic functions.

The brain uses glucose as its principal source of energy. During low glucose states, the brain utilizes ketone bodies as its primary energy source. During exercise, the brain can use lactate as a source of energy.

In the developing brain, neurons follow molecular signals from regulatory cells like astrocytes to determine their location, the type of neurotransmitter they will secrete, and with which neurons they will communicate, leading to the formation of a circuit between neurons that will be in place during adulthood. In the adult brain, developed neurons fit in their corresponding place and develop axons and dendrites to connect with the neighboring neurons. [20]

Neurons communicate via neurotransmitters released into the synaptic space, a 20 to 50-nanometer area between neurons. The neuron that releases the neurotransmitter into the synaptic space is called the presynaptic neuron, and the neuron that receives the neurotransmitter is called the postsynaptic neuron. An action potential in the presynaptic neuron leads to calcium influx and the subsequent release of neurotransmitters from their storage vesicle into the synaptic space. The neurotransmitter then travels to the postsynaptic neuron and binds to receptors to influence its activity. Neurotransmitters are rapidly removed from the synaptic space by enzymes. [21]

The oligodendrocytes in the CNS produce myelin. Myelin forms insulating sheaths around axons to allow the swift travel of electrical impulses through the axons. The nodes of Ranvier are gaps in the myelin sheath of axons, allowing sodium influx into the axon to help maintain the speed of the electrical impulse traveling through the axon. This transmission is called saltatory nerve conduction, the "jumping" of electrical impulses from one node to another. It ensures that electrical signals do not lose their velocity and can propagate long distances without signal deterioration. [22]

• Related Testing

Functional magnetic resonance imaging (fMRI) can track the effects of neural activity and the energy that the brain consumes by measuring components of the metabolic chain. Other techniques, such as single-photon emission computed tomography (SPECT), study cerebral blood flow and neuroreceptors. Positron emission tomography (PET) assesses the glucose metabolism of the brain. [23]  Electroencephalography (EEG) records the brain's electrical activity and is very useful for detecting various brain disorders. Advancements in these techniques have enabled a broader vision and objective perceptions of mental disorders, leading to improved diagnosis, treatment, and prognosis.

• Pathophysiology

Injury to the brain stimulates the proliferation of astrocytes, an immunological response to neurodegenerative disorders called "reactive gliosis." [24]  Damage to neural tissue promotes molecular and morphological changes and is essential in the upregulation of the glial fibrillary acidic protein (GFAP). On the other hand, epidermal growth factor receptor (EGFR) allows the transition from non-reactive to reactive astrocytes, and its inhibition improves axonal regeneration and rapid recovery. This means that when astrocytes are reactive, they proliferate and hypertrophy, leading to glial scar formation.

The microglia represent the immune and support system of the CNS. They are neuroprotective in the young brain but can react abnormally to stimuli in the aged brain and become neurotoxic and destructive, leading to neurodegeneration. [25]  As the brain ages, microglia acquire an increasingly inflammatory and cytotoxic phenotype, generating a hazardous environment for neurons. [26]  Hence, aging is the most critical risk factor for developing neurodegenerative diseases.

The brain is surrounded by cerebrospinal fluid and is isolated from the bloodstream by the blood-brain barrier (BBB). In cases like infectious meningitis and meningoencephalitis, acute inflammation causes a breakdown of the BBB, leading to the influx of blood-borne immune cells into the CNS. In other inflammatory brain disorders such as Alzheimer disease (AD), Parkinson disease (PD), Huntington disease (HD), or X-linked adrenoleukodystrophy, the primary insult is due to degenerative or metabolic processes, and there is no breakdown of the BBB. [27]

Oligodendrocyte loss can occur due to the production of reactive oxygen species or the activation of inflammatory cytokines, causing decreased myelin production and leading to conditions such as multiple sclerosis (MS). [22]

Disturbances in the neurotransmitter systems are related to these substances' production, release, reuptake, or receptor impairments and can cause neurologic or psychiatric disorders. Glutamate is the brain's most abundant excitatory neurotransmitter, while GABA is the primary inhibitory transmitter. Glycine has a similar inhibitory action in the posterior parts of the brain. Acetylcholine aids in processes such as muscle stimulation at the neuromuscular junction (NMJ), digestion, arousal, salivation, and level of attention. Dopamine is involved in the reward and motivational component, motor control, and the regulation of prolactin release. Serotonin influences mood, feelings of happiness, and anxiety. Norepinephrine is involved in arousal, alertness, vigilance, and attention. 

Cerebral oxygen delivery and consumption rates are ten times higher than global body values. [28]  Blood glucose represents the primary energy source for the brain, and the BBB is highly permeable to it. During low glucose states, the body has developed multiple ways to keep blood glucose within the normal range. As the level drops below 80 mg/dL, pancreatic beta-cells decrease insulin secretion to avoid further glucose decrease. If glucose drops further, pancreatic alpha-cells secrete glucagon, and the adrenal medulla releases epinephrine. Glucagon and epinephrine increase blood glucose levels. Cortisol and growth hormone also act to increase glucose, but they depend on the presence of glucagon and epinephrine to work.

• Clinical Significance

Damage to the Cerebrum

• Frontal lobe -  Damage to the frontal lobe causes interruption of the higher functioning brain processes, including social behavior, planning, motivation, and speech production. Individuals with frontal lobe damage may be unable to regulate their emotions, have meaningful or appropriate social interactions, maintain their past personality traits, or make difficult decisions. [29]
• Temporal lobe - The Wernicke area is located in the superior temporal gyrus in an individual's dominant hemisphere, which is the left hemisphere for 95% of people. Damage to the left (dominant) temporal lobe can lead to Wernicke aphasia. This is typically referred to as "word salad" speech, where the patient will speak fluently, but their words and sentences will lack meaning. [30]  Damage to the right (non-dominant) temporal lobe may lead to persistent talking and deficits in nonverbal memory, processing certain aspects of sound or music (tone, rhythm, pitch), and facial recognition (prosopagnosia).
• Parietal lobe -  Damage to the frontal aspect of the parietal lobe may lead to impaired sensation and numbness on the contralateral side of the body. An individual may have difficulty recognizing texture and shape and may be unable to identify a sensation and its location on their body. Damage to the middle aspect of the parietal lobe can lead to right-left disorientation and difficulty with proprioception. Damage to the non-dominant (right) parietal lobe may lead to apraxia (difficulty with performing purposeful motions such as combing hair or brushing teeth) and difficulty with spatial orientation and navigation (they may get lost in a once familiar area). Patients with non-dominant parietal lobe damage, usually from a middle cerebral artery stroke, may neglect the side opposite of the brain damage (usually the left side), which may manifest as only shaving the right side of their face or drawing a clock with all of the numbers on the right side of the circle. [31]
• Occipital lobe -  Damage to the occipital lobe may lead to visual defects, color agnosia (inability to identify colors), movement agnosia (difficulty recognizing object movements), hallucinations, illusions, and the inability to recognize written words (word blindness). 

Damage to the Cerebellum

Damage to the cerebellum can lead to ataxia, dysmetria, dysarthria, scanning speech, dysdiadochokinesis, tremor, nystagmus, and hypotonia. To test for possible cerebellar dysfunction, a bedside neurologic exam is commonly the first step. This exam may include the Romberg test, heel-to-shin test, finger-to-nose test, and rapid alternating movement test. [32]

Damage to the Brainstem

Damage to the brainstem may present as muscle weakness, visual changes, dysphagia, vertigo, speech impairment, pupil abnormalities, insomnia, respiratory depression, or death.

Neurodegenerative Diseases

Neuronal degeneration worsens with age and can affect different areas of the brain leading to movement, memory, and cognition problems.

Parkinson disease (PD) occurs due to the degeneration of the neurons that synthesize dopamine, leading to motor function deficits. Alzheimer disease (AD) occurs due to abnormally folded protein deposition in the brain leading to neuronal degeneration. Huntington disease occurs due to a genetic mutation that increases the production of the neurotransmitter glutamate. Excessive amounts of glutamate lead to the death of neurons in the basal ganglia producing movement, cognitive, and psychiatric deficits. Vascular dementia occurs due to the death of neurons resulting from the interruption of blood supply.

Although neurodegenerative diseases are not classically caused by disturbed metabolism, research has shown that there is a reduction in glucose metabolism in Alzheimer disease. [33]

Demyelinating Diseases

Demyelinating diseases result from damage to the myelin sheath that covers the nerve cells in the white matter of the brain, spinal cord, and optic nerves. For example, multiple sclerosis and leukodystrophies are a consequence of oligodendrocyte damage.

A stroke is caused by an interruption in the blood supply to the brain, which may ultimately lead to neuronal death. This condition can result in one of several neurological problems depending on the affected region.

Brain Death

Neurologic evaluation of brain death is a complicated process that non-specialists and families might misunderstand. [34]  Brain death is the complete and irreversible loss of brain activity, including the brainstem. It requires verification through well-established clinical protocols and the support of specialized tests.

Hypoglycemia

Glucose is the primary energy source responsible for maintaining brain metabolism and function. The most significant amount of glucose is used for information processing by neurons. [35]  The brain requires a continuous supply of glucose as it has limited glucose reserves. CNS symptoms and signs of hypoglycemia include focal neurological deficits, confusion, stupor, seizure, cognitive impairment, or death.

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Brain, Encephalon, Connections of the several parts of the brain, Cerebrum, Cerebellum, Pons, Cerebral; Superior; Middle; Inferior Peduncle, Medulla oblongata Henry Vandyke Carter, Public Domain, via Wikimedia Commons

The Fore-brain or Prosencephalon, Mesal aspect of a brain sectioned in the median sagittal plane, Foramen of Monro, Middle commissure, Taenia thalami, Habenular commissure, Genu, Callosum, Fornix, Septum Lucidum, Plenum, Pons, Oblongata, Thalamus Henry (more...)

Areas of localization on lateral surface of hemisphere. Motor area in red, Area of general sensations in blue, Auditory area in green, Visual area in yellow, Brain, Neurology Henry Vandyke Carter, Public Domain, via Wikimedia Commons

Pathways from the Brain to the Spinal Cord, The motor tract, Anterior nerve roots, Anterior and Lateral cerebrospinal Fasciculus, Decussation of pyramids, Geniculate fibers, Internal capsule, Motor area of cortex Henry Vandyke Carter, Public Domain, via (more...)

Homonculus: sensory & motor Image courtesy S. Bhimji MD

Disclosure: Kenia Maldonado declares no relevant financial relationships with ineligible companies.

Disclosure: Khalid Alsayouri declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

• Cite this Page Maldonado KA, Alsayouri K. Physiology, Brain. [Updated 2023 Mar 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

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• Review Anatomy of the brainstem: a gaze into the stem of life. [Semin Ultrasound CT MR. 2010] Review Anatomy of the brainstem: a gaze into the stem of life. Angeles Fernández-Gil M, Palacios-Bote R, Leo-Barahona M, Mora-Encinas JP. Semin Ultrasound CT MR. 2010 Jun; 31(3):196-219.
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Introductory essay

Written by the educators who created Mapping and Manipulating the Brain, a brief look at the key facts, tough questions and big ideas in their field. Begin this TED Study with a fascinating read that gives context and clarity to the material.

Here is this mass of jelly, three-pound mass of jelly you can hold in the palm of your hand, and it can contemplate the vastness of interstellar space. It can contemplate the meaning of infinity and it can contemplate itself contemplating on the meaning of infinity. VS Ramachandran

The brain may well be our body's most mysterious organ. Unbelievably complex, utterly fascinating, and notoriously difficult to study, we're left wondering: What exactly does the brain do and how does it do it?

Despite two centuries of intensive research, supported in recent decades by impressive technological advances, answers to many of our questions about the brain are still distant. The reason is easy to appreciate: the brain contains more than ten billion cells — a number equivalent to the total human population on Earth — interacting with each other through about 1,000 times as many connections. Imagine that what's going on in your brain is like a shrunk-down version of the global human population interacting through the Internet. The Internet is hard enough to understand even though we created it; now imagine trying to understand a process of similar complexity without the benefit of knowing how it was generated!

As you listen to these TEDTalks and expand your study of neuroscience through other sources, remember that although we might now know a great deal more about the brain than we did at the start of the 19th century, it's a tiny fraction of what there is to know. Bear in mind that many current ideas may prove wrong. Indeed, it's the excitement of generating and testing, and trying to prove or disprove ideas that might explain the great unknown inside our heads that motivates many research neuroscientists around the world.

A brief history of brain science

The Egyptians wrote the first known descriptions of the brain and its anatomy about 3700 years ago, but another 1200 years elapsed before Greek philosophers of the Hippocratic School identified the brain as the organ responsible for our cognitive functions. Around 400 B.C., Hippocrates declared, "Men ought to know that from the brain, and from the brain only, arise our pleasures, joy, laughter and jests, as well as our sorrows, pains, griefs, and tears." However, not everyone agreed: although Plato and Hippocrates thought that the brain was responsible for sensation, intelligence and mental processes, Aristotle believed it was the heart.

Over the next 2500 years, the work of great European intellectuals including Galen of Bergama, Leonardo da Vinci and Rene Descartes improved our understanding of the brain. By the start of the 19th century, the brain's importance as the organ of perception and higher mental function was beyond doubt.

In the early 1800s, scientists made an important conceptual breakthrough when they hypothesized that different brain functions are carried out in specific and distinct brain regions. Brain regionalization, a concept central to several of the TEDTalks we'll watch, remains an important though controversial component of modern neuroscience.

Some of the initial models of brain regionalization were severely misguided, mainly because they were built on little or no evidence. For example, the Viennese physician Franz Joseph Gall (1758-1828) became convinced for the flimsiest of reasons that each of mankind's mental faculties, including our moral and intellectual capabilities, are each controlled by a separate "organ" within the cerebral hemispheres of the brain. The pseudo-science of phrenology that grew out of Gall's claims gained an enormous popular following in the 19th century; advocates believed that skilled practitioners could feel the lumps and bumps on an individual's skull to gain information about the underlying "organs" and thus fully describe the individual's personality and mental abilities.

Although phrenology is now discredited, the fundamental idea that different functions are localized to different areas of the brain turned out to have merit — even if Gall got the details wrong. The story of phrenology also provides a salutary lesson on the dangers of accepting popular beliefs about aspects of brain function and dysfunction that are difficult to critically evaluate through scientific experimentation. Even today, it's common to find that people think they know more than it's currently possible to know about how and why brains work or go wrong; for example, the causes and cures for various types of mental illness, which may contribute to the social stigma that surrounds these conditions.

Through the late 19th and early 20th centuries, scientists including Pierre Paul Broca, Carl Wernicke, Korbinian Brodmann and Wilder Penfield found credible scientific evidence supporting the subdivision of the brain into discrete areas with different specific functions. Their work was based on studies of patients with localized lesions of the brain, of the anatomical differences between different parts of the brain and of the effects of stimulating discrete brain regions on bodily actions. Together, scientists such as these laid the foundations of modern neuroscience. As you watch the TEDTalks in Mapping and Manipulating the Brain , notice how the speakers reference some of the same approaches used by Broca, Wernicke, Brodmann and Penfield, and how they apply the concepts of brain regionalization and localization of function . Bear in mind, however, that although these concepts are useful, they're also controversial -- more on this below.

How brains are built

Spanish scientist Santiago Ramón Y Cajal (1852-1934) is often thought of as the father of modern neuroscience. Through his extensive and beautiful studies of the microscopic structure of the brain, he discovered that the neuron is the fundamental unit of the nervous system. Since Ramón Y Cajal's breakthrough, scientists have sought to understand how the billions of neurons in the brain are organized to support so many complex functions.

This daunting task would likely be easier if we could follow the process by which the brain is generated, but following brain development is very difficult to do in humans. Thus, we often have to infer how the human brain develops by studying the developing brains of other species, so-called "model organisms" selected for their particular advantages in certain experimental procedures. Aside from helping us to work out how the adult brain functions, research on brain development is a major area in neuroscience for other reasons as well. For example, many conditions like schizophrenia and autism can be traced back to abnormalities in earlier brain development.

The great molecular, structural and functional diversity of brain cells, along with their specializations and precise interactions, are acquired in an organized way through processes that build on differences between the relatively small numbers of cells in the early embryo. As more and more cells are generated in a growing organism, new cells diversify in specific ways as a result of interactions with pre-existing cells, continually adding to the organism's complexity in a highly regulated manner. To understand how brains develop we need to know how their cells develop in specific and reproducible ways as a result of their own internal mechanisms interacting with an expanding array of stimuli from outside the cell.

Since, as discussed above, regionalization is a prominent organizing feature in mature brains, when and how is it established during brain development? Some of the most exciting research on brain development in recent years has focused on this question.

For neurons to develop regional identities, they must possess or acquire information on where they are located within the brain so that they can take on the appropriate specializations. How neurons gain positional information has been one of the most prominent themes in developmental neuroscience in the last 50 years or so, as indeed it has in the broader field of developmental biology (positional identity is required not only by brain cells).

The model that has dominated current thinking was famously elaborated in the 1960s by Lewis Wolpert in his French flag analogy. Here, a signal produced by a group of organizer cells diffuses from its source through a surrounding field of cells. In so doing, it forms a concentration gradient with more of the signal present in areas closer to the source. Cells respond to the concentration of this signal. In Wolpert's French Flag analogy, they become blue, white or red (in reality, they would become cells of different types, not different colors). Close to the source, cells receive signals above the highest threshold (to become blue, or type 1). Beyond this, cells respond to a lower dose (to become white, or type 2) while farther still cells do not receive enough of the signal to respond (and become red, or type 3). Here the model is expressed in terms of three outcomes, but there might be a different number of outcomes depending on the locations and/ or stages of development. The important point is that cells can work out where they are based on the level of signal they receive and they respond accordingly by developing different attributes.

Beyond Wolpert's basic model, the issue of how brain regionalization develops is an important question and we have relatively few answers. Regional specification is a prerequisite for the development of the connections that must link each region of the brain in a stereotypical and highly precise way (but allowing room for plasticity at a fine level). How these trillions of connections are made is another of life's great mysteries.

The connectome and connectionism

Since Ramón Y Cajal's first description of the neuron, scientists have vastly expanded our understanding of the structure and function of these individual building blocks of the brain. However, as Tim Berners-Lee comments, this is just the first step in understanding how our brains really work: "There are billions of neurons in our brains, but what are neurons? Just cells. The brain has no knowledge until connections are made between neurons. All that we know, all that we are, comes from the way our neurons are connected."

You'll hear about the "connectome" in Sebastian Seung's TEDTalk. The suffix "–ome" is used with increasing frequency to indicate a complete collection of whatever units are specified in the first part of the word, such as genes (hence genome), proteins (proteome) or connections (connectome). The connectome of the human brain is bewildering in its complexity, but the development of new brain imaging methods has catalyzed the first serious attempts to map it in living brains. At present, the resolution of imaging methods that can be applied to living brains isn't sufficient to follow individual connections (called axons). In these TEDTalks you'll hear about an attempt to come at the problem from the other direction, using very high resolution imaging of non-living brain tissue to reconstruct the ultramicroscopic anatomy of connections around individual cells. The extent to which these approaches are likely to succeed remains controversial.

The theory known as connectionism addresses a somewhat different matter within the field of brain organization: the relationship between connectivity and function. Essentially, the idea is that higher mental processes such as object recognition, memory and language result from the activity of the connections between areas of the brain rather than the activity of specific discrete regions. Whereas connectionists would agree that primary sensory and motor functions (i.e. responses to sensory stimuli and the activation of movements) are strongly localized to defined areas within the brain, they argue that this applies less clearly at higher cognitive levels. The theory emphasizes the relationship between connected brain areas and the function of the brain as a whole, with all parts having the potential to contribute to cognitive function. You should appreciate, therefore, that there is as yet no accepted view of the extent to which our higher mental functions are localized to particular parts of the brain. It is worth remembering this as you listen to the TEDTalks; keep an open mind on these truly fascinating issues.

Ways of studying brain function

In these TEDTalks, you're going to hear about some of the ways in which we can work out what the human brain does and how it does it. One longstanding approach is to examine what happens when people suffer brain lesions. Phineas Gage, a Vermont railroad worker, provides one spectacular historical example from 1848. Gage was packing gunpowder into a hole when it exploded, blowing the tamping rod through the front of his brain. Astonishingly, he survived and recovered, but those closest to him claimed that he had a very different personality. From this example, scientists hypothesized that elements of human personality are localized to the frontal lobes.

In Jill Bolte Taylor's TEDTalk, you'll hear how Taylor's own stroke provides further evidence for localization of brain function. A few words of caution, however: when we study the effects of a lesion on the brain, we're really learning about what the rest of the brain does without the damaged part, which is not quite the same as what the damaged structure itself does. Maybe this seems rather subtle, but in some cases it becomes important, for example if a lesion causes other parts of the brain to alter what they do.

You'll also hear about powerful techniques for observing the activity of living brains, for example using functional magnetic resonance imaging (FMRI; see the TEDTalk by Oliver Sacks). And you'll hear about methods for looking at the fine structure of neurons in post-mortem material, as in Sebastian Seung's TEDTalk. All have advantages and limitations, but together they give ever- increasing insight into the workings of the human mind.

Let's begin the TEDTalks with neuroanatomist Jill Bolte Taylor, who provides a basic overview of the brain and describes what she learned firsthand about its structure and function when at age 37 she suffered a massive hemorrhage in the left hemisphere of her brain.

Jill Bolte Taylor

My stroke of insight, relevant talks.

VS Ramachandran

3 clues to understanding your brain.

Oliver Sacks

What hallucination reveals about our minds.

Sebastian Seung

I am my connectome.

Christopher deCharms

A look inside the brain in real time.

A light switch for neurons

Rebecca Saxe

How we read each other's minds.

Choose Your Test

Sat / act prep online guides and tips, the 3 major parts of the brain and what they do.

General Education

Mission control. Command center. Control tower. No, I'm not talking about space or your laptop hard drive, or even airport flight control. I'm talking about the human brain—the most complex and essential organ our bodies have. What is the brain structure? What part of the brain controls emotions?

Whether you're studying it in class, preparing for an AP exam, or just curious about brain structure, in this article, you'll learn about the main parts of brain anatomy and their functions and as well as get a general overview of the brain's supporting cast.

What Is the Brain and Why Does It Matter?

The brain is a three-pound organ that serves as headquarters for our bodies. Without it, we wouldn't be able to process information, move our limbs, or even breathe . Together with the spinal cord, brain structure and function helps control the central nervous system—the main part of two that make up the human nervous system. (The other part, the peripheral nervous system, is made up of nerves and neurons that connect the central nervous system to the body's limbs and organs.) The human nervous system is responsible for helping us think, breathe, move, react and feel.

Like any good command center, there is a structure to the brain and its operations that help it carry out its basic functions.

What Are the Main Parts of the Brain?

There are three main parts of the brain: the cerebrum, cerebellum and the brain stem.

Image source: Denise Wawrzyniak , used under CC BY-NC 4.0

What Is the Cerebrum?

Was I A Bee /Wikimedia Commons

The cerebrum is the largest part of the brain. Located in the front and middle part of the brain, it accounts for 85% of the brain's weight. Of the three main parts of the brain, the cerebrum is considered the most recent to develop in human evolution. The cerebrum is responsible for all voluntary actions (e.g.: motor skills), communication, emotions, creativity, intelligence and personality.

What Are the Main Parts of the Cerebrum?

The cerebrum's structure is made up of:

What Are the Layers of the Cerebrum?

The cerebrum has two layers: one inner and one outer . The outer layer is known as the cerebral cortex (represented in red in the spinning image above). Most times, whenever you see photos of the brain, you are looking at the cerebral cortex. This area houses the brain's "gray matter," and is considered the "seat" of human consciousness. Higher brain functions such as thinking, reasoning, planning, emotion, memory, the processing of sensory information and speech all happen in the cerebral cortex. In other words, the cerebral cortex is what sets humans apart from other species.

The cerebral cortex is referred to as "gray matter," due to its color and is responsible for several vital functions, such as those listed above.

What Is the Corpus Callosum?

The cerebrum's inner core houses the brain's "white matter." The major part of the inner core is known as the corpus callosum. The corpus callosum is a thick tract of fibrous nerves that serve as a kind of switchboard enabling the brain's hemispheres to communicate with one another. Whereas the cerebral cortex is the cerebrum's outer layer made up of gray matter, and is responsible for thinking, motor function and information processing; the corpus callosum is the cerebrum's inner core, made up of white matter, with four parts of nerve tracts connecting to different parts of the hemispheres.

Home of the white matter: corpus callosum./ Life Sciences Database /Wikimedia Commons

The corpus callosum's nerve fibers (or axons) are coated with myelin. This fatty substance helps increase the transmission of information between the next part of the cerebrum: the two hemispheres.

The Cerebrum's Left and Right Hemispheres

In addition to two layers, the cerebrum also has two halves, or hemispheres: the left hemisphere and the right hemisphere. Although each hemisphere is known for managing different functions, it is important to note that both handle most processes of the brain structure.

The existence of the hemispheres is vital to our body's functions. The relationship between our brain and body is contralateral. This means, generally speaking, that the left side of the brain (left hemisphere) controls the right side of the body, and the right side of the brain (right hemisphere) controls the left side of the body. Because the hemispheres carry out different tasks, they need to "talk" to one another in real time to coordinate our movements, thoughts, etc.

The left hemisphere is responsible for controlling the right side of the body. It handles language, reasoning, logic and speech. If the left hemisphere were a set of classes in school, it would be your math, science, and English classes.

The right hemisphere is responsible for controlling the left side of the body. It handles spatially-related tasks and visual understanding. In terms of classes, the right hemisphere would be your arts, music, and creative writing classes.

The deep groove separating the hemispheres is called the longitudinal fissure (or, cerebral fissure).

The longitudinal fissure is prevented from completely splitting the cerebrum in half by the corpus callosum. Thanks to the corpus callosum (our brain's speedy switchboard), the left side of your brain can chat instantaneously with the right side of your brain.

The red line down the center of the cerebrum is the longitudinal fissure. Life Sciences Database /Wikimedia Commons

All this hemisphere talk brings us to the final part of the cerebrum: the four lobes.

What Are the 4 Lobes of the Brain?

Database Center for Life Sciences /Wikimedia Commons

The cerebrum's left and right hemispheres are each divided into four lobes: the frontal, parietal, occipital and temporal lobes. The lobes generally handle different functions, but much like the hemispheres, the lobes don't function alone. The lobes are separated from each other by depressions in the cortex known as sulcus (or sulci) and are protected by the skull with bones named after their corresponding lobes.

Cancer Research UK /Wikimedia Commons

The frontal lobe is located in the front of the brain, running from your forehead to your ears. It is responsible for problem-solving and planning, thought, behavior, speech, memory and movement. The frontal lobe is separated from the parietal lobe by the central sulcus and is protected by a singular frontal skull bone.

The parietal lobe picks up where the frontal lobe ends and goes until the mid-back part of the brain (about where a ponytail would be). It is responsible for processing information from the senses (touch, sight, hearing, smelling and sight), as well as language interpretation and spatial perception. It is separated from the other lobes on all four sides: from the frontal lobe by central sulcus; from the opposite hemisphere by the longitudinal fissure; from the occipital lobe by parieto-occipital sulcus; and from the temporal lobe below by a depression known as the lateral sulcus, or lateral fissure. Because each hemisphere has a parietal lobe, there are two parietal skull bones—one on the external side of each hemisphere.

The occipital lobe is located in the back of the brain. It is considered the brain's "visual processing center" because it's where the bulk of information our eyes take in gets analyzed and sorted. It is separated from the parietal lobe by the parieto-occipital sulcus; from the temporal lobe by the lateral occipital sulcus; and from the cerebellum (the second part of the brain, coming up soon) by what is called the cerebellar tentorium (or tentorium cerebelli). It is protected by the skull's singular occipital bone.

The temporal lobe is located in behind and below the frontal lobe (and beneath the parietal lobe), under the lateral fissure. It is responsible for our memory, emotions, language and speech, and auditory and visual processing. It is separated from the parietal and frontal lobe by the lateral sulcus (lateral fissure); from the occipital lobe by the lateral occipital sulcus and occipitotemporal sulcus; and is adjacent to the corpus callosum. Similar to its parietal neighbor, the temporal lobe is protected by two bones—one temporal bone on the external side of each hemisphere.

The brain's lobes serve as a map for understanding where brain functions happen. Image source: Denise Wawrzyniak , used under CC BY-NC 4.0

What Is the Cerebellum?

The cerebellum stands for "little brain" in Latin. It looks like a separate mini-brain behind and underneath the cerebrum (beneath the temporal and occipital lobes) and above the brain stem. The cerebellum (along with the brain stem) is considered evolutionarily to be the oldest part of the brain.

Where the cerebrum makes up 85% of the brain's mass, the cerebellum takes up only 10%. However, the cerebellum accounts for more than half of the brain's neurons. The cerebellum is responsible for voluntary movements, coordination, balance, posture, muscle tone, and cognitive functions.

What Are the Main Parts of the Cerebellum?

The cerebellum's structure is made up of:

The Cerebellum's Inner and Outer Layers

Like the cerebrum, the cerebellum has two layers: one inner and one outer. The outer layer is called the cerebellar cortex. Like the cerebral cortex, it is full of gray matter. Functions such as movement, motor learning, balance and posture happen here.

Underneath the cortex lies the cerebellum's white matter. Called "arbor vitae" ("tree of life") for its appearance, the cerebellum's white matter contains cerebellar nuclei. These neurons are vital because they relay information between the cerebral cortex and the peripheral nervous system to assist in learning and cognitive functions, motor control, balance and coordination. (In a very loose parallel, both the cerebellar nuclei of the cerebellum and the corpus callosum of the cerebrum are responsible for internal communications: The corpus callosum relays messages between there cerebrum's hemispheres, and the cerebellar nuclei relays messages between the body and cerebrum.)

The Cerebellum's Left and Right Hemispheres

The cerebellum also has two hemispheres: the left cerebellar hemisphere and the right cerebellar hemisphere. Just as the longitudinal fissure divides the cerebrum's hemispheres, the "vermis" (Latin for "worm") separates the cerebellum's hemispheres.

The Database Center for Life Science /Wikimedia Commons

Cerebellar hemispheres seen from front (r) and back (l)/ The Database Center for Life Science/ Wikimedia Commons

What Are the Three Lobes of the Cerebellum?

The cerebellum's hemispheres are each divided into three lobes: the anterior lobe, posterior lobe, and the flocculonodular lobe. These lobes are split up by two fissures (grooves), called the primary fissure and the posterolateral fissure.

The three lobes of the Cerebellum, where purple is the anterior lobe, green is the posterior lobe and orange is the Flocculonodular lobe. /Database Center for Life Science /Wikimedia Commons

Unlike the cerebral cortex, there are no clear separation of functions in the cerebellar cortex. The best way to identify the tasks are by the information each section processes.

Spinocerebellum

The anterior lobe and the vermis together are known as the spinocerebellum. The spinocerebellum helps regulate muscle tone and body movement. It's also responsible for our sense of our body's position in relation to our surroundings, and in relation to other parts of our body (a.k.a.: proprioceptive information). This area receives input from our spinal cord, auditory and visual systems.

Cerebrocerebellum

The posterior lobe (the cerebellar hemispheres at large, not including the vermis and anterior lobe) is called the cerebrocerebellum. This area is responsible for planning movements that are about to happen, managing sensory information to determine action and motor learning. It receives information from the cerebral cortex (the parietal lobe).

Vestibulocerebellum

The flocculonodular lobe is referred to as the vestibulocerebellum. This area is responsible for managing our eye movement and balance. Unlike the other two areas, this one gets data directly from a sensory nerve, the vestibular nerve. (The vestibular nerve is connected to the vestibular system, which is responsible for our sense of balance and spatial orientation.) This area receives information from the visual cortex.

What Are the Four Nuclei of the Cerebellum?

As the three lobes take in information from the cerebrum, spinal cord and body, the cerebellum also has a way of sending out information. This is done through what are called nuclei—a bundle or neurons embedded deep in the cerebellum's white matter.

Rounding out cerebellum's composition are the four nuclei that pass information between the cerebrum and the body. These nuclei are: dentate, emboliform, globose, and fastcgi. They receive on the body and give information from the cerebellum through Purkinje cells (neurons) and mossy fibers.

What Is the Brain Stem?

Life Sciences Database /Wikimedia Commons

The final section of the brain is a mass of tissue and nerves called the brain stem. Located underneath the cerebrum and cerebellum, the brain stem connects the brain to the spinal cord. All information that goes from the brain to the body (or vice versa), must pass through the brain stem to reach its destination. The brain stem accounts for the remaining 5% of the brain's mass, and is (along with the cerebellum), the oldest part of the brain. The brain stem is responsible for regulating the heart and lungs, communications between the brain and the peripheral nervous system (the nerves of the body), our sleep cyc le, and coordinating reflexes.

The brain stem plugs the brain (central nervous system) into the rest of the body through the spinal cord (peripheral nervous system).

Running throughout the brain stem is an area known as the "reticular formation." This collection of nuclei plays a vital role in managing our consciousness (e.x.: sleep and alertness) and connecting with the various motor nerves to help us move our heads and faces, regulate our involuntary actions, and to help us chew, eat, breathe and see.

What Are the Main Parts of the Brain Stem?

The brain stem is made up of three parts: the midbrain, the pons and the medulla.

BruceBlaus /Wikimedia Commons

Life Sciences Database/ Wikimedia Commons

The midbrain is located underneath the cerebral cortex, near the top of the brain stem. It connects the cerebrum to the brain stem. The midbrain helps process visual and auditory information, such as controlling the eyes and eyelids. It also plays a role in regulating our body temperature and motor movements.

Main Parts of the Midbrain

Pons is the Latin word for "bridge." The pons is responsible for connecting the brain stem to the cerebral cortex and the cerebrum to the cerebellum. It can be found right underneath the midbrain and above the medulla oblongata. Although it is the largest section of the brain stem, the pons is only about 2.5 centimeters long. The pons is responsible for assisting in motor functions, particularly for nerves in the face, ears, and eyes. It also plays a role in regulating the intensity and frequency of breathing. It has both gray and white matter, but it does share gray matter with the midbrain. The reticular formation of the pons' gray matter plays a vital role in dreaming and REM (deep) sleep.

Medulla Oblongata

The medulla oblongata is located behind and partially underneath the cerebellum. It is responsible for our life-sustaining involuntary (autonomic) actions such as breathing, regulating the heartbeat and blood pressure, and reflexes such as sneezing, vomiting and coughing.

Like the pons, the medulla also has gray and white matter. Some of its white matter is shared with the spinal cord, while its gray matter processes cranial nerve information. The reticular formation in the medulla's gray matter assists with breathing and controlling the heart rate.

The Cerebellar Peduncles

Earlier, we learned how four nuclei are responsible for connecting the cerebellum to the body. To connect the cerebellum to the brain stem, the brain depends on nerve tracts called cerebellar peduncles. The cerebellar peduncles help process and analyze motor and sensory information, such as the position of our joints and limbs. There are six cerebellar peduncles (three for each hemisphere) with both white and gray matter. The six cerebellar peduncles are: superior (2), middle (2) and inferior (2).

What Are the Regions of the Brain and How Do They Fit Into the Brain Structure?

The three main parts of the brain are split amongst three regions developed during the embryonic period: the forebrain, midbrain and hindbrain. Together, these regions act as a useful map to understanding the various parts of the brain's structure and functions.

The forebrain, midbrain and hindbrain serve as regions that make finding the various parts of the brain easier./ BruceBlaus /Wikimedia Commons

To better understand the roles of the forebrain, midbrain and hindbrain within the brain, check out the short video below:

The Brain's Support System

While we've covered the basics of brain anatomy, there are a few other supporting players that assist the brain in its role as our command center.

Protective cushioning

Arielinson /Wikimedia Commons

The brain is surrounded by the cranium, or skull. The skull's job is to house the brain and protect its soft tissue from trauma and the elements. The skull is made up of 22 bones, along with fibrous joints called sutures, that keep the brain safe from external injury.

Cushioning the brain from the skull are the meninges. The meninges are three layers of tissue known as the dura mater, arachnoid & pia mater. These layers protect the brain from being displaced; separate the cerebrum from the cerebellum; transfer food and waste from the brain to the body; and clean the brain's fluid to keep it running.

Food and Waste Transport

The cerebrospinal fluid is responsible for bringing in nutrients and removing waste in the brain and spinal cord. It is found in the meninges layers and is moved through the brain by ventricles.

The brain's four main ventricles (spaces) help the cerebrospinal fluid nourish and cleanse the brain. They also cushion the brain from injury.

Information Transport and Boundary Assistants

The gyrus (plural: gyri) and sulcus (sulci) are what give the brain its wrinkly appearance. The grooves (or fissures) of the brain are known as the sulci, while the bumps (or ridges) are called the gyri. These folds and ridges help increase how much of the cerebral cortex can fit into the skull. They also create boundaries between the different sections of the brain, such as the two hemispheres and four lobes of the cerebrum.

Albert Kok /Wikimedia Commons

The gyri and sulci create the wrinkles we traditionally associate with the brain./ Bruce Blaus /Wikimedia Commons

The heart pumps blood to the brain through two arteries: the carotid and vertebral. Because of the brain's importance to the body and the fact that brain cells die without constant blood flow, the heart sends about 20% of the body's bloody supply to the brain. The blood brings oxygen and other nutrients the brain needs to regulate itself and function properly.

The heart pumps blood in and out of the body through the carotid and vertebral arteries.

Neurons and Glial Cells

The human brain has about 80-100 billion neurons, and roughly the same of glial cells. Neurons and glial cells help coordinate and transport signals within the human nervous system. While neurons communicate and receive information with cells, glial cells protect and support neurons in completing their mission.

Cranial Nerves

Twelve cranial nerves help transport information from the brain and body. These motor and sensory nerves are part of the peripheral nervous system and are responsible for controlling muscles and processing information from the organs and bringing it to the brain. These include our senses of sight and smell, as well as our balance and hearing.

The twelve nerves are named for their function and include: the olfactory nerve, optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducens nerve, facial nerve, vestibulocochlear nerve, glossopharyngeal nerve, vagus nerve, spinal accessory nerve, and hypoglossal nerve.

In Conclusion: Brain Anatomy

The human brain is an incredibly complex, hardworking organ. As one-half of the human nervous system, the brain structure oversees nearly all of the body's operations, including how we move, think, feel and understand ourselves and the world around us. And knowing all this brain anatomy is important. From the cerebrum, cerebellum and the brain stem, to all the parts in between: this three-pound organ is what makes us humans, well, human.

What's Next?

Want to gain medical experience before starting college ? Check out 59 medical programs available for high school students .

Prepping for an AP Biology exam and need some help? Find out what books you need with our Best AP Biology Books of 2019 .

Interested in medical school? Learn what it takes to become a medical student with our guide to pre-med and the main requirements for medical school .

Brittany Logan graduated from Columbia University Graduate School of Journalism with a Master of Science with Honors. She has a dual-degree Master's from Sciences Po School of Journalism in Paris, and earned her Bachelor’s in Global Studies from the University of California, Santa Barbara. She has spent several years working in higher education- including as an English teacher abroad and as a teaching assistant in science writing at Columbia University’s Earth Institute.

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Nih research matters.

May 21, 2024

Unseen details of human brain structure revealed

At a glance.

• Researchers generated a high-resolution map of all the cells and connections in a single cubic millimeter of the human brain.
• The results reveal previously unseen details of brain structure and provide a resource for further studies.

Fully understanding how the human brain works requires knowing the relationships between the various cells that make up the brain. This entails visualizing the brain’s structure on the scale of nanometers in order to see the connections between neurons.

A team of researchers, led by Dr. Jeff Lichtman at Harvard University and Dr. Viren Jain at Google Research, used electron microscopy (EM) to image a cubic millimeter-sized piece of human brain tissue at high resolution. The tissue was removed from the cerebral cortex of a patient as part of a surgery for epilepsy.

The team began by cutting the tissue into more than 5,000 slices, or sections, each of which was then imaged by EM. This yielded about 1.4 petabytes, or 1,400 terabytes, of data. Using these data, the researchers generated a 3D reconstruction of almost every cell in the sample. Results of the NIH-funded study appeared in Science on May 10, 2024.

Analysis of individual cells in the sample revealed a total of more than 57,000 cells. Most of these were either neurons, which send electrical signals, or glia, which provide various support functions to the neurons. Glia outnumbered neurons 2-to-1. The most common glial cells were oligodendrocytes, which provide structural support and electrical insulation to neurons. The one cubic mm sample also contained about 230 mm of blood vessels.

The reconstruction revealed structural details not seen before. The researchers analyzed a type of neuron, called triangular cells, that are found in the deepest layer of the cerebral cortex. Many of these adopted one of two orientations, which were mirror images of each other. The significance of this organization remains unknown.

The team used machine learning to identify synapses—the junctions through which signals pass from one cell to another. They found almost 150 million synapses. Almost all neurons formed only one synapse with a given target cell. But a small fraction formed two or more synapses to the same target. In at least one case, more than 50 synapses connected a single pair of cells. Although rare, connections of seven or more synapses between cells were much more common than expected by chance. This suggests that these strong connections have some functional significance.

The results illustrate just how complex the brain is at the cellular level. They also show the value of connectomics—the science of generating comprehensive maps of connections between brain cells—for understanding brain function.

“The word ‘fragment’ is ironic,” Lichtman says. “A terabyte is, for most people, gigantic, yet a fragment of a human brain—just a miniscule, teeny-weeny little bit of human brain—is still thousands of terabytes.”

The team has made their dataset available to the public. They have also provided various software tools to help examine the brain map. The hope is that further study of the data, by this team and others, will yield new insight into the workings of the human brain.

“This incredible advancement—the ability to capture and process over 1,000 terabytes of data from the brain—wouldn’t have been possible without a study participant’s generous donation and the important partnerships between neuroscientists, computer scientists, and engineers,” says Dr. John Ngai, director of NIH’s BRAIN Initiative. “These collaborations are central in our aim of building a full map of the human brain so we can bring cures closer to the clinic.”

—by Brian Doctrow, Ph.D.

Related Links

• Scientists Build Largest Maps to Date of Cells in Human Brain
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• 3-D Model of Human Brain Development and Disease
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• The Brain Research Through Advancing Innovative Neurotechnologies® (BRAIN) Initiative

References:  A petavoxel fragment of human cerebral cortex reconstructed at nanoscale resolution. Shapson-Coe A, Januszewski M, Berger DR, Pope A, Wu Y, Blakely T, Schalek RL, Li PH, Wang S, Maitin-Shepard J, Karlupia N, Dorkenwald S, Sjostedt E, Leavitt L, Lee D, Troidl J, Collman F, Bailey L, Fitzmaurice A, Kar R, Field B, Wu H, Wagner-Carena J, Aley D, Lau J, Lin Z, Wei D, Pfister H, Peleg A, Jain V, Lichtman JW. Science . 2024 May 10;384(6696):eadk4858. doi: 10.1126/science.adk4858. Epub 2024 May 10. PMID: 38723085.

Funding:  NIH’s BRAIN Initiative, National Institute of Mental Health (NIMH), National Institute of Neurological Disorders and Stroke (NINDS), and National Institute of Biomedical Imaging and Bioengineering (NIBIB); Stanley Center for Psychiatric Research at the Broad Institute; National Science Foundation; Intelligence Advanced Research Projects Activity.

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Divisions of the Brain: Forebrain, Midbrain, Hindbrain

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The  brain  is a complex organ that acts as the control center of the body. As a component of the  central nervous system , the brain sends, receives, processes, and directs sensory information. The brain is split into left and right hemispheres by a band of fibers called the  corpus callosum . There are three major divisions of the brain, with each division performing specific functions. The major divisions of the brain are the forebrain (or prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon).

Forebrain (Prosencephalon)

BSIP / Getty Images

The forebrain is by far the largest brain division. It includes the cerebrum , which accounts for about two-thirds of the brain's mass and covers most other brain structures. The forebrain consists of two subdivisions called the telencephalon and diencephalon. The olfactory and optic cranial nerves are found in the forebrain, as well as the lateral and third cerebral ventricles .

Telencephalon

A major component of the telencephalon is the cerebral cortex , which is further divided into four lobes. These lobes include the frontal lobes, parietal lobes, occipital lobes, and temporal lobes. The cerebral cortex contains folded bulges called gyri that create indentations in the brain. Functions of the cerebral cortex include processing sensory information, controlling motor functions, and performing higher-order functions such as reasoning and problem-solving.

• Frontal Lobes :  The prefrontal cortex, premotor area, and motor area of the brain. These lobes function in voluntary muscle movement, memory, thinking, decision-making, and planning.
• Parietal Lobes : Responsible for receiving and processing sensory information . These lobes also contain the somatosensory cortex, which is essential for processing touch sensations.
• Occipital Lobes :  Responsible for receiving and processing visual information from the retina.
• Temporal Lobes :  Home of the  limbic system structures, including the amygdala and hippocampus . These lobes organize sensory input and aid in auditory perception, memory formation, and language and speech production.

Diencephalon

The diencephalon is the region of the brain that relays sensory information and connects components of the endocrine system with the nervous system . The diencephalon regulates a number of functions including autonomic, endocrine, and motor functions. It also plays a major role in sensory perception. Components of the diencephalon include:

• Thalamus :  A  limbic system structure that connects areas of the cerebral cortex that are involved in sensory perception and movement with other parts of the brain and spinal cord. The thalamus also plays a role in the control of sleep and wake cycles.
• Hypothalamus : Acts as the control center for many autonomic functions including respiration, blood pressure, and body temperature regulation. This endocrine structure secretes hormones that act on the pituitary gland to regulate biological processes including metabolism, growth, and the development of reproductive system organs . As a component of the limbic system, the hypothalamus influences various emotional responses through its influence on the pituitary gland, skeletal muscular system, and autonomic nervous system.
• Pineal Gland : This small endocrine gland produces the hormone melatonin. Production of this hormone is vital to the regulation of sleep-wake cycles and also influences sexual development. The pineal gland converts nerve signals from the sympathetic component of the peripheral nervous system into hormone signals, thereby linking the nervous and endocrine systems.

Midbrain (Mesencephalon)

MediaForMedical / Getty Images

The  midbrain  is the area of the brain that connects the forebrain to the hindbrain. The midbrain and hindbrain together compose the brainstem . The brainstem connects the spinal cord with the cerebrum. The midbrain regulates movement and aids in the processing of auditory and visual information. The oculomotor and trochlear cranial nerves are located in the midbrain. These nerves control eye and eyelid movement. The cerebral aqueduct, a canal that connects the third and fourth cerebral ventricles , is also located in the midbrain. Other components of the midbrain include:

• Tectum: The dorsal portion of the midbrain that is composed of the superior and inferior colliculi. These colliculi are rounded bulges that are involved in visual and auditory reflexes. The superior colliculus processes visual signals and relays them to the occipital lobes. The inferior colliculus processes auditory signals and relays them to the auditory cortex in the temporal lobe.
• Cerebral peduncle:  The anterior portion of the midbrain consisting of large bundles of nerve fiber tracts that connect the forebrain to the hindbrain. Structures of the cerebral peduncle include the tegmentum and crus cerebri. The tegmentum forms the base of the midbrain and includes the reticular formation and the red nucleus. The reticular formation is a cluster of nerves within the brainstem that relay sensory and motor signals to and from the spinal cord and the brain. It aids in the control of autonomic and endocrine functions, as well as muscle reflexes and sleep and awake states. The red nucleus is a mass of cells that aids in motor function.
• Substantia nigra:  This large mass of brain matter with pigmented nerve cells produces the neurotransmitter dopamine. The substantia nigra helps control voluntary movement and regulates mood.

Hindbrain (Rhombencephalon)

Encyclopaedia Britannica / Getty Images

The hindbrain is composed of two subregions called the metencephalon and myelencephalon. Several cranial nerves are located in this brain region. The trigeminal, abducent, facial, and vestibulocochlear nerves are found in the metencephalon. The glossopharyngeal, vagus, accessory, and hypoglossal nerves are located in the myelencephalon. The fourth cerebral ventricle also extends through this region of the brain. The hindbrain assists in the regulation of autonomic functions, maintaining balance and equilibrium, movement coordination, and the relay of sensory information.

Metencephalon

The metencephalon is the upper region of the hindbrain and contains the pons and cerebellum. The pons is a component of the brainstem, which acts as a bridge connecting the cerebrum with the medulla oblongata and cerebellum. The pons assists in the control of autonomic functions, as well as states of sleep and arousal.

The cerebellum relays information between muscles and areas of the cerebral cortex that are involved in motor control. This hindbrain structure aids in fine movement coordination, balance and equilibrium maintenance, and muscle tone.

Myelencephalon

The myelencephalon is the lower region of the hindbrain located below the metencephalon and above the spinal cord. It consists of the medulla oblongata . This brain structure relays motor and sensory signals between the spinal cord and higher brain regions. It also assists in the regulation of autonomic functions such as breathing, heart rate , and reflex actions including swallowing and sneezing.

• Anatomy of the Brain
• Brainstem: Function and Location
• Anatomy of the Cerebellum and its Function
• Get a Description and Diagram of Thalamus Gray Matter
• Functions of the Central Nervous System
• Anatomy of the Brain: Your Cerebrum
• Hypothalamus Activity and Hormone Production
• Where in the Brain Is the Pons
• Overview of the Medulla Oblongata
• Basic Parts of the Brain and Their Responsibilities
• Learn About the Mesencephalon (Midbrain) Function and Structures
• Diencephalon Section of the Brain
• The Limbic System of the Brain
• White Matter and Your Brain
• Types of Cells in the Human Body
• Third Ventricle

Essay on Human Brain

Students are often asked to write an essay on Human Brain in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Human Brain

The human brain: an overview.

The human brain is a complex organ, responsible for all our thoughts, feelings, and actions. It’s made up of billions of nerve cells, or neurons, which communicate through electrical signals.

Parts of the Brain

The brain is divided into three main parts: the cerebrum, cerebellum, and brainstem. The cerebrum is the largest part and controls thinking, learning, and emotions. The cerebellum manages balance and coordination. The brainstem connects the brain to the spinal cord and controls automatic functions like breathing.

Brain’s Functionality

The brain is always active, even during sleep. It processes information from our senses, helps us understand the world around us, and makes decisions. It’s truly a remarkable organ!

250 Words Essay on Human Brain

Introduction.

The human brain, a marvel of biological engineering, is the most complex organ in the human body. It is the epicenter of human consciousness, responsible for our thoughts, emotions, and actions.

Structure and Function

The brain is divided into three main parts: the cerebrum, cerebellum, and brainstem. The cerebrum, the largest part, is responsible for higher brain functions such as thought, emotion, and sensory processing. The cerebellum coordinates motor functions, while the brainstem controls automatic functions like heart rate and breathing.

Neuroplasticity

A remarkable feature of the brain is its neuroplasticity, the ability to form and reorganize synaptic connections in response to learning, experience, or injury. This adaptability underscores the brain’s capacity for lifelong learning and recovery.

Cognitive Abilities

Cognitive abilities such as memory, attention, and problem-solving are facilitated by the brain’s intricate network of neurons. These abilities enable us to navigate and interpret the world around us, engage in social interactions, and make decisions.

Brain and Technology

Advancements in technology have led to breakthroughs in understanding the brain. Techniques like fMRI and EEG provide detailed insights into brain activity, paving the way for treatments of neurological disorders.

The human brain, with its intricate structure and impressive capabilities, continues to be a subject of fascination and study. Its complexity and adaptability underscore the limitless potential of human cognition, making it a cornerstone of our identity as a species.

500 Words Essay on Human Brain

Introduction to the human brain.

The human brain, a product of millions of years of evolutionary progression, is a marvel of biological engineering. It is a complex organ, responsible for controlling all the functions of the human body, processing sensory information, and coordinating responses. The brain is an intricate network of billions of neurons, which communicate and work together to generate our thoughts, feelings, and actions.

Structural Complexity of the Brain

The human brain is composed of several distinct regions, each with specific functions. The cerebrum, the largest part, is responsible for higher cognitive functions like thinking, learning, and consciousness. It is divided into two hemispheres, each further subdivided into four lobes: the frontal lobe, parietal lobe, occipital lobe, and temporal lobe.

The cerebellum, located beneath the cerebrum, coordinates motor control, balance, and coordination. The brainstem, connecting the brain to the spinal cord, controls automatic functions vital for survival, such as heartbeat, breathing, and digestion.

Neurons: The Building Blocks

Neurons, the fundamental units of the brain, transmit information through electrical and chemical signals. They consist of a cell body, dendrites, and an axon. The dendrites receive signals from other neurons, which are then passed through the cell body and down the axon to the next neuron. This communication forms neural networks, the basis for all brain activity.

Brain Plasticity

One of the most fascinating aspects of the human brain is its plasticity, the ability to reorganize itself by forming new neural connections throughout life. This adaptability allows us to learn new skills, adapt to changes, and recover from brain injuries. Neuroplasticity underscores the brain’s remarkable capacity for resilience and growth.

The Brain and Consciousness

The brain is not only a biological organ but also the seat of consciousness and identity. It is responsible for our thought processes, emotions, memories, and perceptions. The intricate interplay of neural networks generates the rich tapestry of human experience, from the most mundane thoughts to the most profound creative insights.

Future Research Directions

Despite significant advances in neuroscience, much about the brain remains a mystery. Key questions about consciousness, memory formation, and the nature of intelligence are yet to be fully answered. The development of advanced neuroimaging techniques and computational models offers exciting possibilities for future research.

Understanding the brain is not merely an academic exercise but has profound implications for treating neurological disorders, improving education, and even addressing ethical questions about artificial intelligence and brain-computer interfaces.

In conclusion, the human brain, with its intricate architecture and dynamic functionality, is a testament to the complexity and beauty of human life. As we continue to unravel its mysteries, we deepen our understanding of what it means to be human, highlighting the importance of continued research in this fascinating field.

That’s it! I hope the essay helped you.

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• What is brain health...

What is brain health and why is it important?

Read our brain health collection.

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• Peer review
• Yongjun Wang , professor 1 2 ,
• Yuesong Pan , associate professor 1 2 ,
• Hao Li , professor 1 2
• 1 Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, Beijing, China
• 2 China National Clinical Research Center for Neurological Diseases, Beijing, China
• Correspondence to: Y Wang yongjunwang{at}ncrcnd.org.cn

Yongjun Wang and colleagues discuss the definition of brain health and the opportunities and challenges of future research

The human brain is the command centre for the nervous system and enables thoughts, memory, movement, and emotions by a complex function that is the highest product of biological evolution. Maintaining a healthy brain during one’s life is the uppermost goal in pursuing health and longevity. As the population ages, the burden of neurological disorders and challenges for the preservation of brain health increase. It is therefore vital to understand what brain health is and why it is important. This article is the first in a series that aims to define brain health, analyse the effect of major neurological disorders on brain health, and discuss how these disorders might be treated and prevented.

Definition of brain health

Currently, there is no universally recognised definition of brain health. Most existing definitions have only a general description of normal brain function or emphasise one or two dimensions of brain health. The US Centers for Disease Control and Prevention defined brain health as an ability to perform all the mental processes of cognition, including the ability to learn and judge, use language, and remember. 1 The American Heart Association/American Stroke Association (AHA/ASA) presidential advisory defined optimal brain health as “average performance levels among all people at that age who are free of known brain or other organ system diseases in terms of decline from function levels, or as adequacy to perform all activities that the individual wishes to undertake.” 2

The brain is a complex organ and has at least three levels of functions that affect all aspects of our daily lives: interpretation of senses and control of movement; maintenance of cognitive, mental, and emotional processes; and maintenance of normal behaviour and social cognition. Brain health may therefore be defined as the preservation of optimal brain integrity and mental and cognitive function at a given age in the absence of overt brain diseases that affect normal brain function.

Effect of major neurological disorders on brain health

Several neurological disorders may disrupt brain function and affect humans’ health. Medically, neurological disorders that cause brain dysfunction can be classified into three groups:

Brain diseases with overt damage to brain structures, such as cerebrovascular diseases, traumatic brain injury, brain tumours, meningitis, and communication and sensory disorders

Functional brain disorders with detectable destruction of brain connections or networks, such as neurodegenerative diseases (eg, Parkinson’s disease, Alzheimer’s disease, and other dementias) and mental disorders (eg, schizophrenia, depression, bipolar disorder, alcoholism, and drug abuse)

Other brain disorders without detectable structural or functional impairment, such as migraine and sleep disorders.

These neurological disorders may have different or common effects on brain health and function. For instance, Alzheimer’s disease is the main type of dementia, with a decline in different domains of cognitive function. Mood disorders may cause dysfunction in execution, reward processing, and emotional regulations. In addition to physical disability, aphasia, gait and balance problems, and cerebrovascular diseases may lead to cognitive impairment and dementia, which are neglected by both patients and physicians.

Ageing and burden of neurological disorders

Human ageing is mainly reflected in the aspects of brain ageing and degradation of brain function. The number of people aged 60 years and over worldwide was around 900 million in 2015 and is expected to grow to two billion by 2050. 3 With the increases in population ageing and growth, the burden of neurological disorders and challenges to the preservation of brain health steeply increase. People with neurological disorders will have physical disability, cognitive or mental disorders, and social dysfunction and be a large economic burden.

Globally, neurological disorders were the leading cause of disability adjusted life years (276 million) and the second leading cause of death (9 million) in 2016, according to the Global Burden of Diseases study. 4 Stroke, migraine, Alzheimer’s disease and other dementias, and meningitis are the largest contributors to neurological disability adjusted life years. 4 About one in four adults will have a stroke in their lifetime, from the age of 25 years onwards. 5 Roughly 50 million people worldwide were living with dementia in 2018, and the number will more than triple to 152 million by 2050. 6 In the following decades, governments will face increasing demand for treatment, rehabilitation, and support services for neurological disorders.

Opportunities and challenges of future research on brain health

Opportunities and challenges exist in the assessment of brain health, the mechanism of brain function and dysfunction, and approaches to promote brain health ( box 1 ).

Lack of metrics or tools to comprehensively assess or quantify brain health

Little knowledge about the mechanisms of brain function and dysfunction

Few effective approaches to prevent and treat brain dysfunction in some major neurological disorders, such as dementia

Need to precisely preserve brain functions for people with neurosurgical diseases

Defining and promoting optimal brain health require the scientific evaluation of brain health. However, it is difficult to comprehensively evaluate or quantify brain health through one metric owing to the multidimensional aspects of brain health. Many structured or semistructured questionnaires have been developed to test brain health by self-assessments or close family member assessments of daily function or abilities. In recent decades new structural and functional neuroimaging techniques have been applied to evaluate brain network integrity and functional connectivity. 7 However, these subjective or objective measures have both strengths and weaknesses. For instance, scales such as the mini-mental state examination and Montreal cognitive assessment are simple and easy to implement but are used only as global screening tools for cognitive impairment; tests such as the digit span, Rey-Osterrieth complex figure test, trail making A and B, Stroop task, verbal fluency test, Boston naming test, and clock drawing test are used mainly to assess one or two specific domains of memory, language, visuospatial, attention, and executive function; and neuroimaging techniques, although non-invasive and objective, still have disadvantages of test contraindications, insufficient temporal or spatial resolution, motion artefact, and high false discovery rates, which limit their clinical transformation.

Another difficulty in measuring brain health is that age, culture, ethnicity, and geography specific variations exist in the perception of optimal brain health. Patient centred assessment of brain function, such as self-perception of cognitive function and quality of life, should also be considered when measuring brain health. 8 Universal acceptable, age appropriate, multidimensional, multidisciplinary, and sensitive metrics or tools are required to comprehensively measure and monitor brain function and brain health.

To promote optimal brain health, we need a better understanding of the mechanisms of brain function and dysfunction. Unfortunately, little is known about the working mechanism of the brain. Although we have made considerable developments in neuroscience in recent decades, we still cannot totally decipher the relations between spatiotemporal patterns of activity across the interconnected networks of neurons and thoughts or the cognitive and mental state of a person. 9 Recent progress in brain simulation and artificial intelligence provides a vital tool to understand biological brains, and vice versa. 10 11 The development of brain inspired computation, brain simulation, and intelligent machines was emphasised in the European Union and China Brain Project. 9 12

Meanwhile, the mechanisms behind the brain dysfunction in some neurological disorders are still not well understood, especially for mental and neurodegenerative disorders. Further investigation of the mechanisms of brain diseases may indicate approaches to treatment and improve brain function. Brain imaging based cognitive neuroscience may unravel the underlying brain mechanism of cognitive dysfunction and provide an avenue to develop a biological framework for precision biomarkers of mood disorders. 13

Most common neurological diseases, such as cerebrovascular diseases and Alzheimer’s disease, have complex aetiopathologies, typically involving spatial-temporal interactions of genetic and environmental factors. However, a single genetic factor could account for the disease progression of monogenic neurological disorders. These diseases could be more readily investigated by simplified cross species modelling, leading to better understanding of their mechanisms and greater efficiency in testing innovative therapies. Such research may provide a window to promote the investigation of common neurological disorders and general brain health, as discussed by Chen and colleagues elsewhere in this series. 14

Few effective approaches are available to prevent and treat brain dysfunction in some major neurological disorders, such as dementia. Neurons are not renewable, and brain dysfunction is always irreversible. Recent trials targeting amyloid clearance and the selective inhibition of tau protein aggregation failed to improve cognition or modify disease progression in patients with mild Alzheimer’s disease. 15 16 More attention has focused on other potential therapeutic targets, such as vascular dysfunction, inflammation, and the gut microbiome, as discussed by Shi and colleagues. 17 In particular, recent studies showed that the early impairment of cognition was induced by the disruption of neurovascular unit integrity, which may cause hypoperfusion and the breakdown of the blood-brain barrier and subsequent impairment in the clearance of proteins in the brain. 18 19 Physical activity, mental exercise, a healthy diet and nutrition, social interaction, ample sleep and relaxation, and control of vascular risk factors are considered six pillars of brain health. The AHA/ASA presidential advisory recommended the AHA’s Life’s Simple 7 (non-smoking, physical activity, healthy diet, appropriate body mass index, blood pressure, total cholesterol, and blood glucose) to maintain optimal brain health. 2 Pan and colleagues discuss how this may indicate a new dawn of preventing some cognitive impairment and brain dysfunction by preventing vascular risk factors or cerebrovascular diseases. 20

For other neurological disorders with potential therapeutic approaches, the main aim is to preserve brain function. Impaired brain function due to anatomical structural damage is underestimated in patients with neurosurgical diseases such as brain tumours, trauma, and epilepsy. In recent years, treatment targets for neurosurgical diseases have changed from focusing on survival or life expectancy to balancing brain structures and functions. Precise preservation of brain function requires an understanding of the exquisite relation between brain structure and function and advanced technologies to visualise brain structure-function relations. 21

Another example of the predicament associated with protection of brain function is uncertainty in the treatment response in epilepsy management. Current standard care for epilepsy relies on a trial and error approach of sequential regimens of antiseizure medications. The time delay due to this treatment approach means that such treatments may be less effective and irreversible damage may occur. Chen and colleagues 22 describe how recent advances in personalised epilepsy management based on artificial intelligence, genomics, and patient derived stem cells are bringing some hope to overcome this predicament in epilepsy management and promise a more effective strategy. 23 24

Brain health is the maintenance of multidimensional aspects of brain function. However, several neurological disorders may affect brain health in one or more aspects of brain function. Deciphering and promoting the function and health of the brain, the most mysterious organ in the human body, will have a dramatic impact on science, medicine, and society. 25 In the past seven years, a number of large scale brain health initiatives have been launched in several countries to promote the development of neuroscience, brain simulation, and brain protection. 9 However, further challenges are raised by the different key research directions of brain projects in different countries. In the face of these challenges, Liu and colleagues argue that collaboration on brain health research is urgently needed. 26 As the other articles in this series describe, coordinated research has enormous potential to improve the prognosis of brain disorders.

Key messages

Brain health is the preservation of optimal brain integrity and mental and cognitive function and the absence of overt neurological disorders

Human ageing increases the burden of brain dysfunction and neurological diseases and the demands for medical resources

Further studies are required to assess brain health, understand the mechanism of brain function and dysfunction, and explore effective approaches to promote brain health.

Contributors and sources: YW proposed the idea for this series on brain health. YW and YP drafted the first manuscript. All the authors critically reviewed and revised the manuscript. YP and HL expertise is in the area of clinical research methods and clinical research on stroke. YW is an expert in clinical research on stroke and neurological diseases. YW is the guarantor.

Competing interests We have read and understood BMJ policy on declaration of interests and declare that the study was supported by grants from the National Science and Technology Major Project (2017ZX09304018), National Key R&D Program of China (2018YFC1312903, 2017YFC1310902, 2018YFC1311700, and 2018YFC1311706), National Natural Science Foundation of China (81971091), Beijing Hospitals Authority Youth Programme (QML20190501), and Beijing Municipal Science and Technology Commission (D171100003017002).

Provenance and peer review: Commissioned; externally peer reviewed.

This article is part of a series launched at the Chinese Stroke Association annual conference on 10 October 2020, Beijing, China. Open access fees were funded by the National Science and Technology Major Project. The BMJ peer reviewed, edited, and made the decision to publish these articles.

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/ .

• ↵ Centers for Disease Control and Prevention. Healthy aging. What is a healthy brain? New research explores perceptions of cognitive health among diverse older adults. https://www.cdc.gov/aging/pdf/perceptions_of_cog_hlth_factsheet.pdf
• Gorelick PB ,
• Iadecola C ,
• American Heart Association/American Stroke Association
• ↵ WHO Global Health Ethics team. Ageing. https://www.who.int/ethics/topics/ageing/en/ . 2019
• GBD 2016 Neurology Collaborators.
• Feigin VL ,
• GBD 2016 Lifetime Risk of Stroke Collaborators
• ↵ Alzheimer’s Disease International. World Alzheimer report 2018. The state of the art of dementia research: new frontiers. https://www.alz.co.uk/research/world-report-2018
• Gordon MF ,
• Lenderking WR ,
• Patient-Reported Outcome Consortium’s Cognition Working Group
• Ullman TD ,
• Tenenbaum JB ,
• Gershman SJ
• Hassabis D ,
• Kumaran D ,
• Summerfield C ,
• Botvinick M
• Capitão L ,
• Satterthwaite TD ,
• Thomas RG ,
• Alzheimer’s Disease Cooperative Study Steering Committee ,
• Solanezumab Study Group
• Gauthier S ,
• Feldman HH ,
• Schneider LS ,
• Sabbagh MN ,
• Henstridge CM ,
• Spires-Jones TL
• Sweeney MD ,
• Montagne A ,
• Zlokovic BV
• Wardlaw JM ,
• Couldwell WT ,
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Home — Essay Samples — Nursing & Health — Human Brain — Anatomy of the Brain

Anatomy of The Brain

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Parts of the Brain Involved with Memory

Learning objectives.

• Explain the brain functions involved in memory; recognize the roles of the hippocampus, amygdala, and cerebellum in memory

Are memories stored in just one part of the brain, or are they stored in many different parts of the brain? Karl Lashley began exploring this problem, about 100 years ago, by making lesions in the brains of animals such as rats and monkeys. He was searching for evidence of the engram : the group of neurons that serve as the “physical representation of memory” (Josselyn, 2010). First, Lashley (1950) trained rats to find their way through a maze. Then, he used the tools available at the time—in this case a soldering iron—to create lesions in the rats’ brains, specifically in the cerebral cortex. He did this because he was trying to erase the engram, or the original memory trace that the rats had of the maze.

Lashley did not find evidence of the engram, and the rats were still able to find their way through the maze, regardless of the size or location of the lesion. Based on his creation of lesions and the animals’ reaction, he formulated the equipotentiality hypothesis : if part of one area of the brain involved in memory is damaged, another part of the same area can take over that memory function (Lashley, 1950). Although Lashley’s early work did not confirm the existence of the engram, modern psychologists are making progress locating it. Eric Kandel, for example, spent decades working on the synapse, the basic structure of the brain, and its role in controlling the flow of information through neural circuits needed to store memories (Mayford, Siegelbaum, & Kandel, 2012).

Many scientists believe that the entire brain is involved with memory. However, since Lashley’s research, other scientists have been able to look more closely at the brain and memory. They have argued that memory is located in specific parts of the brain, and specific neurons can be recognized for their involvement in forming memories. The main parts of the brain involved with memory are the amygdala, the hippocampus, the cerebellum, and the prefrontal cortex (Figure 1).

First, let’s look at the role of the amygdala in memory formation. The main job of the amygdala is to regulate emotions, such as fear and aggression. The amygdala plays a part in how memories are stored because storage is influenced by stress hormones. For example, one researcher experimented with rats and the fear response (Josselyn, 2010). Using Pavlovian conditioning, a neutral tone was paired with a foot shock to the rats. This produced a fear memory in the rats. After being conditioned, each time they heard the tone, they would freeze (a defense response in rats), indicating a memory for the impending shock. Then the researchers induced cell death in neurons in the lateral amygdala, which is the specific area of the brain responsible for fear memories. They found the fear memory faded (became extinct). Because of its role in processing emotional information, the amygdala is also involved in memory consolidation: the process of transferring new learning into long-term memory. The amygdala seems to facilitate encoding memories at a deeper level when the event is emotionally arousing.

Link to Learning

In this TED Talk called “A Mouse. A Laser Beam. A Manipulated Memory,” Steve Ramirez and Xu Liu from MIT talk about using laser beams to manipulate fear memory in rats. Find out why their work caused a media frenzy once it was published in Science .

Hippocampus

Another group of researchers also experimented with rats to learn how the hippocampus functions in memory processing. They created lesions in the hippocampi of the rats, and found that the rats demonstrated memory impairment on various tasks, such as object recognition and maze running. They concluded that the hippocampus is involved in memory, specifically normal recognition memory as well as spatial memory (when the memory tasks are like recall tests) (Clark, Zola, & Squire, 2000). Another job of the hippocampus is to project information to cortical regions that give memories meaning and connect them with other connected memories. It also plays a part in memory consolidation: the process of transferring new learning into long-term memory.

Injury to this area leaves us unable to process new declarative memories. One famous patient, known for years only as H. M., had both his left and right temporal lobes (hippocampi) removed in an attempt to help control the seizures he had been suffering from for years (Corkin, Amaral, González, Johnson, & Hyman, 1997). As a result, his declarative memory was significantly affected, and he could not form new semantic knowledge. He lost the ability to form new memories, yet he could still remember information and events that had occurred prior to the surgery.

View this Slate video for a closer look at how memory works, as well as how researchers are now studying H. M.’s brain.

Cerebellum and Prefrontal Cortex

Although the hippocampus seems to be more of a processing area for explicit memories, you could still lose it and be able to create implicit memories (procedural memory, motor learning, and classical conditioning), thanks to your cerebellum. For example, one classical conditioning experiment is to accustom subjects to blink when they are given a puff of air. When researchers damaged the cerebellums of rabbits, they discovered that the rabbits were not able to learn the conditioned eye-blink response (Steinmetz, 1999; Green & Woodruff-Pak, 2000).

Other researchers have used brain scans, including positron emission tomography (PET) scans, to learn how people process and retain information. From these studies, it seems the prefrontal cortex is involved. In one study, participants had to complete two different tasks: either looking for the letter a in words (considered a perceptual task) or categorizing a noun as either living or non-living (considered a semantic task) (Kapur et al., 1994). Participants were then asked which words they had previously seen. Recall was much better for the semantic task than for the perceptual task. According to PET scans, there was much more activation in the left inferior prefrontal cortex in the semantic task. In another study, encoding was associated with left frontal activity, while retrieval of information was associated with the right frontal region (Craik et al., 1999).

Neurotransmitters

There also appear to be specific neurotransmitters involved with the process of memory, such as epinephrine, dopamine, serotonin, glutamate, and acetylcholine (Myhrer, 2003). There continues to be discussion and debate among researchers as to which neurotransmitter plays which specific role (Blockland, 1996). Although we don’t yet know which role each neurotransmitter plays in memory, we do know that communication among neurons via neurotransmitters is critical for developing new memories. Repeated activity by neurons leads to increased neurotransmitters in the synapses and more efficient and more synaptic connections. This is how memory consolidation occurs.

It is also believed that strong emotions trigger the formation of strong memories, and weaker emotional experiences form weaker memories; this is called arousal theory (Christianson, 1992). For example, strong emotional experiences can trigger the release of neurotransmitters, as well as hormones, which strengthen memory; therefore, our memory for an emotional event is usually better than our memory for a non-emotional event. When humans and animals are stressed, the brain secretes more of the neurotransmitter glutamate, which helps them remember the stressful event (McGaugh, 2003). This is clearly evidenced by what is known as the flashbulb memory phenomenon.

Learn more about flashbulb memories in this brief video.

You can view the transcript for “Flashbulb Memories” here (opens in new window) .

A flashbulb memory is an exceptionally clear recollection of an important event (Figure 2). Where were you when you first heard about the 9/11 terrorist attacks? Most likely you can remember where you were and what you were doing. In fact, a Pew Research Center (2011) survey found that for those Americans who were age 8 or older at the time of the event, 97% can recall the moment they learned of this event, even a decade after it happened.

Dig Deeper: Inaccurate and False Memories

I was sitting there, and my Chief of Staff—well, first of all, when we walked into the classroom, I had seen this plane fly into the first building. There was a TV set on. And you know, I thought it was pilot error and I was amazed that anybody could make such a terrible mistake. (Greenberg, 2004, p. 2)

Contrary to what President Bush recalled, no one saw the first plane hit, except people on the ground near the twin towers. The plane hitting the first tower was not initially broadcasted on television because it had been a normal Tuesday morning in New York City until the first plane hit.

Some people attributed Bush’s wrong recall of the event to conspiracy theories. However, there is a much more benign explanation: human memory, even flashbulb memories, can be frail. In fact, memory can be so frail that we can convince a person an event happened to them, even when it did not. In studies, research participants will recall hearing a word, even though they never heard the word. For example, participants were given a list of 15 sleep-related words, but the word “sleep” was not on the list. Participants recalled hearing the word “sleep” even though they did not actually hear it (Roediger & McDermott, 2000). The researchers who discovered this named the theory after themselves and a fellow researcher, calling it the Deese-Roediger-McDermott paradigm.

Think It Over

Describe a flashbulb memory of a significant event in your life.

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• Flashbulb Memory. Authored by : Kara McCord. Located at : https://youtu.be/mPhW9bUI4F0 . License : Other . License Terms : Standard YouTube License
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• Parts of the Brain Involved with Memory. Authored by : OpenStax College. Located at : https://openstax.org/books/psychology-2e/pages/8-2-parts-of-the-brain-involved-with-memory . License : CC BY: Attribution . License Terms : Download for free at https://openstax.org/books/psychology-2e/pages/1-introduction

physical trace of memory

some parts of the brain can take over for damaged parts in forming and storing memories

strong emotions trigger the formation of strong memories and weaker emotional experiences form weaker memories

exceptionally clear recollection of an important event

General Psychology Copyright © by OpenStax and Lumen Learning is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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• 09 May 2024

Cubic millimetre of brain mapped in spectacular detail

• Carissa Wong

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Rendering based on electron-microscope data, showing the positions of neurons in a fragment of the brain cortex. Neurons are coloured according to size. Credit: Google Research & Lichtman Lab (Harvard University). Renderings by D. Berger (Harvard University)

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Researchers have mapped a tiny piece of the human brain in astonishing detail. The resulting cell atlas, which was described today in Science 1 and is available online , reveals new patterns of connections between brain cells called neurons, as well as cells that wrap around themselves to form knots, and pairs of neurons that are almost mirror images of each other.

The 3D map covers a volume of about one cubic millimetre, one-millionth of a whole brain, and contains roughly 57,000 cells and 150 million synapses — the connections between neurons. It incorporates a colossal 1.4 petabytes of data. “It’s a little bit humbling,” says Viren Jain, a neuroscientist at Google in Mountain View, California, and a co-author of the paper. “How are we ever going to really come to terms with all this complexity?”

Slivers of brain

The brain fragment was taken from a 45-year-old woman when she underwent surgery to treat her epilepsy. It came from the cortex, a part of the brain involved in learning, problem-solving and processing sensory signals. The sample was immersed in preservatives and stained with heavy metals to make the cells easier to see. Neuroscientist Jeff Lichtman at Harvard University in Cambridge, Massachusetts, and his colleagues then cut the sample into around 5,000 slices — each just 34 nanometres thick — that could be imaged using electron microscopes.

Jain’s team then built artificial-intelligence models that were able to stitch the microscope images together to reconstruct the whole sample in 3D. “I remember this moment, going into the map and looking at one individual synapse from this woman’s brain, and then zooming out into these other millions of pixels,” says Jain. “It felt sort of spiritual.”

A single neuron (white) shown with 5,600 of the axons (blue) that connect to it. The synapses that make these connections are shown in green. Credit: Google Research & Lichtman Lab (Harvard University). Renderings by D. Berger (Harvard University)

When examining the model in detail, the researchers discovered unconventional neurons, including some that made up to 50 connections with each other. “In general, you would find a couple of connections at most between two neurons,” says Jain. Elsewhere, the model showed neurons with tendrils that formed knots around themselves. “Nobody had seen anything like this before,” Jain adds.

The team also found pairs of neurons that were near-perfect mirror images of each other. “We found two groups that would send their dendrites in two different directions, and sometimes there was a kind of mirror symmetry,” Jain says. It is unclear what role these features have in the brain.

Proofreaders needed

The map is so large that most of it has yet to be manually checked, and it could still contain errors created by the process of stitching so many images together. “Hundreds of cells have been ‘proofread’, but that’s obviously a few per cent of the 50,000 cells in there,” says Jain. He hopes that others will help to proofread parts of the map they are interested in. The team plans to produce similar maps of brain samples from other people — but a map of the entire brain is unlikely in the next few decades, he says.

“This paper is really the tour de force creation of a human cortex data set,” says Hongkui Zeng, director of the Allen Institute for Brain Science in Seattle. The vast amount of data that has been made freely accessible will “allow the community to look deeper into the micro-circuitry in the human cortex”, she adds.

Gaining a deeper understanding of how the cortex works could offer clues about how to treat some psychiatric and neurodegenerative diseases. “This map provides unprecedented details that can unveil new rules of neural connections and help to decipher the inner working of the human brain,” says Yongsoo Kim, a neuroscientist at Pennsylvania State University in Hershey.

Nature 629 , 739-740 (2024)

doi: https://doi.org/10.1038/d41586-024-01387-9

Shapson-Coe, A. et al. Science 384 , eadk4858 (2024).

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Why writing by hand beats typing for thinking and learning

Jonathan Lambert

If you're like many digitally savvy Americans, it has likely been a while since you've spent much time writing by hand.

The laborious process of tracing out our thoughts, letter by letter, on the page is becoming a relic of the past in our screen-dominated world, where text messages and thumb-typed grocery lists have replaced handwritten letters and sticky notes. Electronic keyboards offer obvious efficiency benefits that have undoubtedly boosted our productivity — imagine having to write all your emails longhand.

To keep up, many schools are introducing computers as early as preschool, meaning some kids may learn the basics of typing before writing by hand.

But giving up this slower, more tactile way of expressing ourselves may come at a significant cost, according to a growing body of research that's uncovering the surprising cognitive benefits of taking pen to paper, or even stylus to iPad — for both children and adults.

Is this some kind of joke? A school facing shortages starts teaching standup comedy

In kids, studies show that tracing out ABCs, as opposed to typing them, leads to better and longer-lasting recognition and understanding of letters. Writing by hand also improves memory and recall of words, laying down the foundations of literacy and learning. In adults, taking notes by hand during a lecture, instead of typing, can lead to better conceptual understanding of material.

"There's actually some very important things going on during the embodied experience of writing by hand," says Ramesh Balasubramaniam , a neuroscientist at the University of California, Merced. "It has important cognitive benefits."

While those benefits have long been recognized by some (for instance, many authors, including Jennifer Egan and Neil Gaiman , draft their stories by hand to stoke creativity), scientists have only recently started investigating why writing by hand has these effects.

A slew of recent brain imaging research suggests handwriting's power stems from the relative complexity of the process and how it forces different brain systems to work together to reproduce the shapes of letters in our heads onto the page.

Your brain on handwriting

Both handwriting and typing involve moving our hands and fingers to create words on a page. But handwriting, it turns out, requires a lot more fine-tuned coordination between the motor and visual systems. This seems to more deeply engage the brain in ways that support learning.

Shots - Health News

Feeling artsy here's how making art helps your brain.

"Handwriting is probably among the most complex motor skills that the brain is capable of," says Marieke Longcamp , a cognitive neuroscientist at Aix-Marseille Université.

Gripping a pen nimbly enough to write is a complicated task, as it requires your brain to continuously monitor the pressure that each finger exerts on the pen. Then, your motor system has to delicately modify that pressure to re-create each letter of the words in your head on the page.

"Your fingers have to each do something different to produce a recognizable letter," says Sophia Vinci-Booher , an educational neuroscientist at Vanderbilt University. Adding to the complexity, your visual system must continuously process that letter as it's formed. With each stroke, your brain compares the unfolding script with mental models of the letters and words, making adjustments to fingers in real time to create the letters' shapes, says Vinci-Booher.

That's not true for typing.

To type "tap" your fingers don't have to trace out the form of the letters — they just make three relatively simple and uniform movements. In comparison, it takes a lot more brainpower, as well as cross-talk between brain areas, to write than type.

Recent brain imaging studies bolster this idea. A study published in January found that when students write by hand, brain areas involved in motor and visual information processing " sync up " with areas crucial to memory formation, firing at frequencies associated with learning.

"We don't see that [synchronized activity] in typewriting at all," says Audrey van der Meer , a psychologist and study co-author at the Norwegian University of Science and Technology. She suggests that writing by hand is a neurobiologically richer process and that this richness may confer some cognitive benefits.

Other experts agree. "There seems to be something fundamental about engaging your body to produce these shapes," says Robert Wiley , a cognitive psychologist at the University of North Carolina, Greensboro. "It lets you make associations between your body and what you're seeing and hearing," he says, which might give the mind more footholds for accessing a given concept or idea.

Those extra footholds are especially important for learning in kids, but they may give adults a leg up too. Wiley and others worry that ditching handwriting for typing could have serious consequences for how we all learn and think.

What might be lost as handwriting wanes

The clearest consequence of screens and keyboards replacing pen and paper might be on kids' ability to learn the building blocks of literacy — letters.

"Letter recognition in early childhood is actually one of the best predictors of later reading and math attainment," says Vinci-Booher. Her work suggests the process of learning to write letters by hand is crucial for learning to read them.

"When kids write letters, they're just messy," she says. As kids practice writing "A," each iteration is different, and that variability helps solidify their conceptual understanding of the letter.

Research suggests kids learn to recognize letters better when seeing variable handwritten examples, compared with uniform typed examples.

This helps develop areas of the brain used during reading in older children and adults, Vinci-Booher found.

"This could be one of the ways that early experiences actually translate to long-term life outcomes," she says. "These visually demanding, fine motor actions bake in neural communication patterns that are really important for learning later on."

Ditching handwriting instruction could mean that those skills don't get developed as well, which could impair kids' ability to learn down the road.

"If young children are not receiving any handwriting training, which is very good brain stimulation, then their brains simply won't reach their full potential," says van der Meer. "It's scary to think of the potential consequences."

Many states are trying to avoid these risks by mandating cursive instruction. This year, California started requiring elementary school students to learn cursive , and similar bills are moving through state legislatures in several states, including Indiana, Kentucky, South Carolina and Wisconsin. (So far, evidence suggests that it's the writing by hand that matters, not whether it's print or cursive.)

Slowing down and processing information

For adults, one of the main benefits of writing by hand is that it simply forces us to slow down.

During a meeting or lecture, it's possible to type what you're hearing verbatim. But often, "you're not actually processing that information — you're just typing in the blind," says van der Meer. "If you take notes by hand, you can't write everything down," she says.

The relative slowness of the medium forces you to process the information, writing key words or phrases and using drawing or arrows to work through ideas, she says. "You make the information your own," she says, which helps it stick in the brain.

Such connections and integration are still possible when typing, but they need to be made more intentionally. And sometimes, efficiency wins out. "When you're writing a long essay, it's obviously much more practical to use a keyboard," says van der Meer.

Still, given our long history of using our hands to mark meaning in the world, some scientists worry about the more diffuse consequences of offloading our thinking to computers.

"We're foisting a lot of our knowledge, extending our cognition, to other devices, so it's only natural that we've started using these other agents to do our writing for us," says Balasubramaniam.

It's possible that this might free up our minds to do other kinds of hard thinking, he says. Or we might be sacrificing a fundamental process that's crucial for the kinds of immersive cognitive experiences that enable us to learn and think at our full potential.

Balasubramaniam stresses, however, that we don't have to ditch digital tools to harness the power of handwriting. So far, research suggests that scribbling with a stylus on a screen activates the same brain pathways as etching ink on paper. It's the movement that counts, he says, not its final form.

Jonathan Lambert is a Washington, D.C.-based freelance journalist who covers science, health and policy.

• handwriting

New method to reveal what drives brain diseases

The brain is often referred to as a "black box" -- one that's difficult to peer inside and determine what's happening at any given moment. This is part of the reason why it's difficult to understand the complex interplay of molecules, cells and genes that underly neurological disorders. But a new CRISPR screen method developed at Scripps Research has the potential to uncover new therapeutic targets and treatments for these conditions.

The method, outlined in a study published in Cell on May 20, 2024, provides a way to rapidly examine the brain cell types linked to key developmental genes at a scale never done before -- helping unravel the genetic and cellular drivers of different neurological diseases.

"We know that certain genetic variations in our genome can make us vulnerable or resilient towards different diseases, but which specific cell types are behind a disease? Which brain regions are susceptible to the genome mutations in those cells? These are the kinds of questions we're trying to answer," says senior author Xin Jin, PhD, an assistant professor in the Department of Neuroscience at Scripps Research. "With this new technology, we want to build a more dynamic picture across brain region, across cell type, across the timing of disease development, and really start understanding how the disease happened -- and how to design interventions."

Thanks to over a decade's efforts in human genetics, scientists have had access to long lists of genetic changes that contribute to a range of human illnesses, but knowing how a gene causes a disease is very different than knowing how to treat the illness itself. Every risk gene may impact one or several different cell types. Comprehending how those cell types -- and even individual cells -- impact a gene and affect disease progression is key to understanding how to ultimately treat that disease.

This is why Jin, along with the study's first author, Xinhe Zheng, a PhD candidate and the Frank J. Dixon Graduate Fellow at Scripps Research, co-invented the new technique, named in vivo Perturb-seq. This method leverages CRISPR-Cas9 technology and a readout, single-cell transcriptomic analysis, to measure its impact on a cell: one cell at a time. Using CRISPR-Cas9, scientists can make precise changes to the genome during brain development, and then closely study how those changes affect individual cells using single-cell transcriptomic analysis -- for tens of thousands of cells in parallel.

"Our new system can measure individual cells' response after genetic perturbations, meaning that we can paint a picture of whether certain cell types are more susceptible than others and react differently when a particular mutation happens," Jin says.

Previously, the method for introducing the genetic perturbations into the brain tissue was very slow, often taking days or even weeks, which created suboptimal conditions for studying gene functions related to neurodevelopment. But Jin's new screening method allows for rapid expression of perturbation agents in living cells within 48 hours -- meaning scientists can quickly see how specific genes function in different types of cells in a very short amount of time.

The method also enables a level of scalability that was previously impossible -- the research team was able to profile more than 30,000 cells in just one experiment, 10-20 times accelerated from the traditional approaches. In many of the brain regions they examined, such as the cerebellum, they were able to collect tens of thousands of cells that previous labeling methods could not reach.

In a pilot study using this new technology, Jin and her team's interest was piqued when they saw a genetic perturbation elicit different effects when perturbed in different cell types. This is important because those impacted cell types are the sites of action for particular diseases or genetic variants. "Despite their smaller population representations, some low-abundant cell types may have a stronger impact than others by the genetic perturbation, and when we systematically look at other cell types across multiple genes, we see patterns. That's why single-cell resolution -- being able to study every cell and how each one behaves -- can offer us a systematic view," Jin says.

With her new technology in hand, Jin plans to apply it to better understand neuropsychiatric conditions and how certain cell types correspond with various brain regions. Moving forward, Jin says she's excited to see this type of technology applied to additional cell types in other organs in the body to better understand a wide range of diseases in terms of tissue, development and aging.

• Brain Tumor
• Sickle Cell Anemia
• Nervous System
• Brain Injury
• Neuroscience
• Disorders and Syndromes
• Brain-Computer Interfaces
• Brain damage
• Sleep disorder
• Endocrinology
• Gene therapy
• Adult stem cell

Story Source:

Materials provided by Scripps Research Institute . Note: Content may be edited for style and length.

Journal Reference :

• Xinhe Zheng, Boli Wu, Yuejia Liu, Sean K. Simmons, Kwanho Kim, Grace S. Clarke, Abdullah Ashiq, Joshua Park, Jiwen Li, Zhilin Wang, Liqi Tong, Qizhao Wang, Keerthi T. Rajamani, Rodrigo Muñoz-Castañeda, Shang Mu, Tianbo Qi, Yunxiao Zhang, Zi Chao Ngiam, Naoto Ohte, Carina Hanashima, Zhuhao Wu, Xiangmin Xu, Joshua Z. Levin, Xin Jin. Massively parallel in vivo Perturb-seq reveals cell-type-specific transcriptional networks in cortical development . Cell , 2024; DOI: 10.1016/j.cell.2024.04.050

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Strange & offbeat.

R.F.K. Jr. Says Doctors Found a Dead Worm in His Brain

The presidential candidate has faced previously undisclosed health issues, including a parasite that he said ate part of his brain.

Robert F. Kennedy Jr. has emphasized his vitality and relative youth compared with the leading Democratic and Republican candidates. Credit... Eduardo Munoz/Reuters

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By Susanne Craig

• May 8, 2024

In 2010, Robert F. Kennedy Jr. was experiencing memory loss and mental fogginess so severe that a friend grew concerned he might have a brain tumor. Mr. Kennedy said he consulted several of the country’s top neurologists, many of whom had either treated or spoken to his uncle, Senator Edward M. Kennedy, before his death the previous year of brain cancer.

Several doctors noticed a dark spot on the younger Mr. Kennedy’s brain scans and concluded that he had a tumor, he said in a 2012 deposition reviewed by The New York Times. Mr. Kennedy was immediately scheduled for a procedure at Duke University Medical Center by the same surgeon who had operated on his uncle , he said.

While packing for the trip, he said, he received a call from a doctor at NewYork-Presbyterian Hospital who had a different opinion: Mr. Kennedy, he believed, had a dead parasite in his head.

The doctor believed that the abnormality seen on his scans “was caused by a worm that got into my brain and ate a portion of it and then died,” Mr. Kennedy said in the deposition.

Now an independent presidential candidate, the 70-year-old Mr. Kennedy has portrayed his athleticism and relative youth as an advantage over the two oldest people to ever seek the White House: President Biden, 81, and former President Donald J. Trump, 77. Mr. Kennedy has secured a place on the ballots in Utah, Michigan, Hawaii and, his campaign says, California and Delaware. His intensive efforts to gain access in more states could put him in a position to tip the election.

He has gone to lengths to appear hale, skiing with a professional snowboarder and with an Olympic gold medalist who called him a “ripper” as they raced down the mountain. A camera crew was at his side while he lifted weights, shirtless, at an outdoor gym in Venice Beach.

Still, over the years, he has faced serious health issues, some previously undisclosed, including the apparent parasite.

For decades, Mr. Kennedy suffered from atrial fibrillation, a common heartbeat abnormality that increases the risk of stroke or heart failure. He has been hospitalized at least four times for episodes, although in an interview with The Times this winter, he said he had not had an incident in more than a decade and believed the condition had disappeared.

About the same time he learned of the parasite, he said, he was also diagnosed with mercury poisoning, most likely from ingesting too much fish containing the dangerous heavy metal, which can cause serious neurological issues.

“I have cognitive problems, clearly,” he said in the 2012 deposition. “I have short-term memory loss, and I have longer-term memory loss that affects me.”

In the interview with The Times, he said he had recovered from the memory loss and fogginess and had no aftereffects from the parasite, which he said had not required treatment. Asked last week if any of Mr. Kennedy’s health issues could compromise his fitness for the presidency, Stefanie Spear, a spokeswoman for the Kennedy campaign, told The Times, “That is a hilarious suggestion, given the competition.”

The campaign declined to provide his medical records to The Times. Neither President Biden nor Mr. Trump has released medical records in this election cycle. However, the White House put out a six-page health summary for President Biden in February. Mr. Trump released a three-paragraph statement from his doctor in November.

On Wednesday afternoon, hours after this article was published, Mr. Kennedy posted a comment on his X profile. “I offer to eat 5 more brain worms and still beat President Trump and President Biden in a debate,” the post read. “I feel confident in the result even with a six-worm handicap.”

Doctors who have treated parasitic infections and mercury poisoning said both conditions can sometimes permanently damage brain function, but patients also can have temporary symptoms and mount a full recovery.

Some of Mr. Kennedy’s health issues were revealed in the 2012 deposition, which he gave during divorce proceedings from his second wife, Mary Richardson Kennedy. At the time, Mr. Kennedy was arguing that his earning power had been diminished by his cognitive struggles.

Mr. Kennedy provided more details, including about the apparent parasite, in the phone interview with The Times, conducted when he was on the cusp of getting on his first state ballot. His campaign declined to answer follow-up questions.

In the days after the 2010 call from NewYork-Presbyterian, Mr. Kennedy said in the interview, he underwent a battery of tests. Scans over many weeks showed no change in the spot on his brain, he said.

Doctors ultimately concluded that the cyst they saw on scans contained the remains of a parasite. Mr. Kennedy said that he did not know the type of parasite or where he might have contracted it, though he suspected it might have been during a trip through South Asia.

Several infectious disease experts and neurosurgeons said in separate interviews with The Times that, based on what Mr. Kennedy described, they believed it was likely a pork tapeworm larva. The doctors have not treated Mr. Kennedy and were speaking generally.

Dr. Clinton White, a professor of infectious diseases at the University of Texas Medical Branch in Galveston, said microscopic tapeworm eggs are sticky and easily transferred from one person to another. Once hatched, the larvae can travel in the bloodstream, he said, “and end up in all kinds of tissues.”

Though it is impossible to know, he added that it is unlikely that a parasite would eat a part of the brain, as Mr. Kennedy described. Rather, Dr. White said, it survives on nutrients from the body. Unlike tapeworm larvae in the intestines, those in the brain remain relatively small, about a third of an inch.

Some tapeworm larvae can live in a human brain for years without causing problems. Others can wreak havoc, often when they start to die, which causes inflammation. The most common symptoms are seizures, headaches and dizziness.

There are roughly 2,000 hospitalizations for the condition, known as neurocysticercosis, each year in the United States, according to the journal Emerging Infectious Diseases .

Scott Gardner, curator of the Manter Laboratory for Parasitology at the University of Nebraska-Lincoln, said that once any worm is in a brain, cells calcify around it. “And you’re going to basically have almost like a tumor that’s there forever. It’s not going to go anywhere.”

Dr. Gardner said it was possible a worm would cause memory loss. However, severe memory loss is more often associated with another health scare Mr. Kennedy said he had at the time: mercury poisoning.

Mr. Kennedy said he was then subsisting on a diet heavy on predatory fish, notably tuna and perch, both known to have elevated mercury levels. In the interview with The Times, he said that he had experienced “severe brain fog” and had trouble retrieving words. Mr. Kennedy, an environmental lawyer who has railed against the dangers of mercury contamination in fish from coal-fired power plants , had his blood tested.

He said the tests showed his mercury levels were 10 times what the Environmental Protection Agency considers safe.

At the time, Mr. Kennedy also was a few years into his crusade against thimerosal, a mercury-containing preservative used in some vaccines. He is a longtime vaccine skeptic who has falsely linked childhood inoculations to a rise in autism, as well as to other medical conditions .

In the interview, Mr. Kennedy said he was certain his diet had caused the poisoning. “ I loved tuna fish sandwiches. I ate them all the time,” he said.

The Times described Mr. Kennedy’s symptoms to Elsie Sunderland, an environmental chemist at Harvard who has not spoken to Mr. Kennedy and responded generally about the condition.

She said the mercury levels that Mr. Kennedy described were high, but not surprising for someone consuming that quantity and type of seafood.

Mr. Kennedy said he made changes after these two health scares, including getting more sleep, traveling less and reducing his fish intake.

He also underwent chelation therapy, a treatment that binds to metals in the body so they can be expelled. It is generally given to people contaminated by metals, such as lead and zinc, in industrial accidents. Dr. Sunderland said that when mercury poisoning is clearly diet-related, she would simply recommend that the person stop eating fish. But another doctor who spoke to The Times said she would advise chelation therapy for the levels Mr. Kennedy said he had.

Mr. Kennedy’s heart issue began in college, he said, when it started beating out of sync.

In 2001 he was admitted to a hospital in Seattle while in town to give a speech, according to news reports. He was treated, and released the next day. He was hospitalized at least three additional times between September 2011 and early 2012, including once in Los Angeles, he said in the deposition. On that visit, he said, doctors used a defibrillator to shock his heart to reset the rhythm.

He said in the deposition that stress, caffeine and a lack of sleep triggered the condition. “It feels like there’s a bag of worms in my chest. I can feel immediately when it goes out,” he said.

He also said in the deposition and the interview that he had contracted hepatitis C through intravenous drug use in his youth. He said he had been treated and had no lingering effects from the infection.

Mr. Kennedy has spoken publicly about one other major health condition — spasmodic dysphonia, a neurological disorder that causes his vocal cords to squeeze too close together and explains his hoarse, sometimes strained voice.

He first noticed it when he was 42 years old, he said in the deposition. Mr. Kennedy for years made a significant amount of money giving speeches , and that business fell off as the condition worsened, he said.

He told an interviewer last year that he had recently undergone a procedure available in Japan to implant titanium between his vocal cords to keep them from involuntarily constricting.

Susanne Craig is an investigative reporter. She has written about the finances of Donald J. Trump and Robert F. Kennedy Jr. and has been a journalist for more than 30 years. More about Susanne Craig

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