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Henry Gustav Molaison: The Curious Case of Patient H.M. 

Erin Heaning

Clinical Safety Strategist at Bristol Myers Squibb

Psychology Graduate, Princeton University

Erin Heaning, a holder of a BA (Hons) in Psychology from Princeton University, has experienced as a research assistant at the Princeton Baby Lab.

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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.

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.

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Henry Gustav Molaison, known as Patient H.M., is a landmark case study in psychology. After a surgery to alleviate severe epilepsy, which removed large portions of his hippocampus , he was left with anterograde amnesia , unable to form new explicit memories , thus offering crucial insights into the role of the hippocampus in memory formation.

• Henry Gustav Molaison (often referred to as H.M.) is a famous case of anterograde and retrograde amnesia in psychology.
• H. M. underwent brain surgery to remove his hippocampus and amygdala to control his seizures. As a result of his surgery, H.M.’s seizures decreased, but he could no longer form new memories or remember the prior 11 years of his life.
• He lost his ability to form many types of new memories (anterograde amnesia), such as new facts or faces, and the surgery also caused retrograde amnesia as he was able to recall childhood events but lost the ability to recall experiences a few years before his surgery.
• The case of H.M. and his life-long participation in studies gave researchers valuable insight into how memory functions and is organized in the brain. He is considered one of the most studied medical and psychological history cases.

Who is H.M.?

Henry Gustav Molaison, or “H.M” as he is commonly referred to by psychology and neuroscience textbooks, lost his memory on an operating table in 1953.

For years before his neurosurgery, H.M. suffered from epileptic seizures believed to be caused by a bicycle accident that occurred in his childhood. The seizures started out as minor at age ten, but they developed in severity when H.M. was a teenager.

Continuing to worsen in severity throughout his young adulthood, H.M. was eventually too disabled to work. Throughout this period, treatments continued to turn out unsuccessful, and epilepsy proved a major handicap and strain on H.M.’s quality of life.

And so, at age 27, H.M. agreed to undergo a radical surgery that would involve removing a part of his brain called the hippocampus — the region believed to be the source of his epileptic seizures (Squire, 2009).

For epilepsy patients, brain resection surgery refers to removing small portions of brain tissue responsible for causing seizures. Although resection is still a surgical procedure used today to treat epilepsy, the use of lasers and detailed brain scans help ensure valuable brain regions are not impacted.

In 1953, H.M.’s neurosurgeon did not have these tools, nor was he or the rest of the scientific or medical community fully aware of the true function of the hippocampus and its specific role in memory. In one regard, the surgery was successful, as H.M. did, in fact, experience fewer seizures.

However, family and doctors soon noticed he also suffered from severe amnesia, which persisted well past when he should have recovered. In addition to struggling to remember the years leading up to his surgery, H.M. also had gaps in his memory of the 11 years prior.

Furthermore, he lacked the ability to form new memories — causing him to perpetually live an existence of moment-to-moment forgetfulness for decades to come.

In one famous quote, he famously and somberly described his state as “like waking from a dream…. every day is alone in itself” (Squire et al., 2009).

H.M. soon became a major case study of interest for psychologists and neuroscientists who studied his memory deficits and cognitive abilities to better understand the hippocampus and its function.

When H.M. died on December 2, 2008, at the age of 82, he left behind a lifelong legacy of scientific contribution.

Surgical Procedure

Neurosurgeon William Beecher Scoville performed H.M.’s surgery in Hartford, Connecticut, in August 1953 when H.M. was 27 years old.

During the procedure, Scoville removed parts of H.M.’s temporal lobe which refers to the portion of the brain that sits behind both ears and is associated with auditory and memory processing.

More specifically, the surgery involved what was called a “partial medial temporal lobe resection” (Scoville & Milner, 1957). In this resection, Scoville removed 8 cm of brain tissue from the hippocampus — a seahorse-shaped structure located deep in the temporal lobe .

Bilateral resection of the anterior temporal lobe in patient HM.

Further research conducted after this removal showed Scoville also probably destroyed the brain structures known as the “uncus” (theorized to play a role in the sense of smell and forming new memories) and the “amygdala” (theorized to play a crucial role in controlling our emotional responses such as fear and sadness).

As previously mentioned, the removal surgery partially reduced H.M.’s seizures; however, he also lost the ability to form new memories.

At the time, Scoville’s experimental procedure had previously only been performed on patients with psychosis, so H.M. was the first epileptic patient and showed no sign of mental illness. In the original case study of H.M., which is discussed in further detail below, nine of Scoville’s patients from this experimental surgery were described.

However, because these patients had disorders such as schizophrenia, their symptoms were not removed after surgery.

In this regard, H.M. was the only patient with “clean” amnesia along with no other apparent mental problems.

H.M’s Amnesia

H.M.’s apparent amnesia after waking from surgery presented in multiple forms. For starters, H.M. suffered from retrograde amnesia for the 11-year period prior to his surgery.

Retrograde describes amnesia, where you can’t recall memories that were formed before the event that caused the amnesia. Important to note, current research theorizes that H.M.’s retrograde amnesia was not actually caused by the loss of his hippocampus, but rather from a combination of antiepileptic drugs and frequent seizures prior to his surgery (Shrader 2012).

In contrast, H.M.’s inability to form new memories after his operation, known as anterograde amnesia, was the result of the loss of the hippocampus.

This meant that H.M. could not learn new words, facts, or faces after his surgery, and he would even forget who he was talking to the moment he walked away.

However, H.M. could perform tasks, and he could even perform those tasks easier after practice. This important finding represented a major scientific discovery when it comes to memory and the hippocampus. The memory that H.M. was missing in his life included the recall of facts, life events, and other experiences.

This type of long-term memory is referred to as “explicit” or “ declarative ” memories and they require conscious thinking.

In contrast, H.M.’s ability to improve in tasks after practice (even if he didn’t recall that practice) showed his “implicit” or “ procedural ” memory remained intact (Scoville & Milner, 1957). This type of long-term memory is unconscious, and examples include riding a bike, brushing your teeth, or typing on a keyboard.

Most importantly, after removing his hippocampus, H.M. lost his explicit memory but not his implicit memory — establishing that implicit memory must be controlled by some other area of the brain and not the hippocampus.

After the severity of the side effects of H.M.’s operation became clear, H.M. was referred to neurosurgeon Dr. Wilder Penfield and neuropsychologist Dr. Brenda Milner of Montreal Neurological Institute (MNI) for further testing.

As discussed, H.M. was not the only patient who underwent this experimental surgery, but he was the only non-psychotic patient with such a degree of memory impairment. As a result, he became a major study and interest for Milner and the rest of the scientific community.

Since Penfield and Milner had already been conducting memory experiments on other patients at the time, they quickly realized H.M.’s “dense amnesia, intact intelligence, and precise neurosurgical lesions made him a perfect experimental subject” (Shrader 2012).

Milner continued to conduct cognitive testing on H.M. for the next fifty years, primarily at the Massachusetts Institute of Technology (MIT). Her longitudinal case study of H.M.’s amnesia quickly became a sensation and is still one of the most widely-cited psychology studies.

In publishing her work, she protected Henry’s identity by first referring to him as the patient H.M. (Shrader 2012).

In the famous “star tracing task,” Milner tested if H.M.’s procedural memory was affected by the removal of the hippocampus during surgery.

In this task, H.M. had to trace an outline of a star, but he could only trace the star based on the mirrored reflection. H.M. then repeated this task once a day over a period of multiple days.

Over the course of these multiple days, Milner observed that H.M. performed the test faster and with fewer errors after continued practice. Although each time he performed the task, he had no memory of having participated in the task before, his performance improved immensely (Shrader 2012).

As this task showed, H.M. had lost his declarative/explicit memory, but his unconscious procedural/implicit memory remained intact.

Given the damage to his hippocampus in surgery, researchers concluded from tasks such as these that the hippocampus must play a role in declarative but not procedural memory.

Therefore, procedural memory must be localized somewhere else in the brain and not in the hippocampus.

H.M’s Legacy

Milner’s and hundreds of other researchers’ work with H.M. established fundamental principles about how memory functions and is organized in the brain.

Without the contribution of H.M. in volunteering the study of his mind to science, our knowledge today regarding the separation of memory function in the brain would certainly not be as strong.

Until H.M.’s watershed surgery, it was not known that the hippocampus was essential for making memories and that if we lost this valuable part of our brain, we would be forced to live only in the moment-to-moment constraints of our short-term memory .

Once this was realized, the findings regarding H.M. were widely publicized so that this operation to remove the hippocampus would never be done again (Shrader 2012).

H.M.’s case study represents a historical time period for neuroscience in which most brain research and findings were the result of brain dissections, lesioning certain sections, and seeing how different experimental procedures impacted different patients.

Therefore, it is paramount we recognize the contribution of patients like H.M., who underwent these dangerous operations in the mid-twentieth century and then went on to allow researchers to study them for the rest of their lives.

Even after his death, H.M. donated his brain to science. Researchers then took his unique brain, froze it, and then in a 53-hour procedure, sliced it into 2,401 slices which were then individually photographed and digitized as a three-dimensional map.

Through this map, H.M.’s brain could be preserved for posterity (Wb et al., 2014). As neuroscience researcher Suzanne Corkin once said it best, “H.M. was a pleasant, engaging, docile man with a keen sense of humor, who knew he had a poor memory but accepted his fate.

There was a man behind the data. Henry often told me that he hoped that research into his condition would help others live better lives. He would have been proud to know how much his tragedy has benefitted science and medicine” (Corkin, 2014).

Corkin, S. (2014). Permanent present tense: The man with no memory and what he taught the world. Penguin Books.

Hardt, O., Einarsson, E. Ö., & Nader, K. (2010). A bridge over troubled water: Reconsolidation as a link between cognitive and neuroscientific memory research traditions. Annual Review of Psychology, 61, 141–167.

Scoville, W. B., & Milner, B. (1957). Loss of recent memory after bilateral hippocampal lesions . Journal of neurology, neurosurgery, and psychiatry, 20 (1), 11.

Shrader, J. (2012, January). HM, the man with no memory | Psychology Today. Retrieved from, https://www.psychologytoday.com/us/blog/trouble-in-mind/201201/hm-the-man-no-memory

Squire, L. R. (2009). The legacy of patient H. M. for neuroscience . Neuron, 61 , 6–9.

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The five steps of EBP

Now that we have identified why evidence-based practice is important, let’s address the steps of evidence-based practice. There are five steps of evidence-based practice that provide a framework for approaching a question, also known as the Five A’s:

• Step 1: Ask a well-built question
• Step 2: Acquire evidence
• Step 3: Appraise the evidence
• Step 4: Apply the evidence along with clinical judgment and patient values
• Step 5: Assess the results

Evidence-Based Practice Copyright © by Various Authors - See Each Chapter Attribution is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

Section Quiz

1.1 what is sociology.

Which of the following best describes sociology as a subject?

• The study of individual behavior
• The study of cultures
• The study of society and social interaction
• The study of economics

C. Wright Mills once said that sociologists need to develop a sociological __________ to study how society affects individuals.

• imagination

A sociologist defines society as a group of people who reside in a defined area, share a culture, and who:

• work in the same industry
• speak different languages
• practice a recognized religion

Seeing patterns means that a sociologist needs to be able to:

• compare the behavior of individuals from different societies
• compare one society to another
• identify similarities in how social groups respond to social pressure
• compare individuals to groups

1.2 The History of Sociology

Which of the following was a topic of study in early sociology?

Which founder of sociology believed societies changed due to class struggle?

• Emile Comte
• Herbert Spencer

Weber believed humans could not be studied purely objectively because they were influenced by:

• their culture
• their genetic makeup
• the researcher

1.3 Theoretical Perspectives in Sociology

Which of these theories is most likely to look at the social world on a micro level?

• Structural functionalism
• Conflict theory
• Symbolic interactionism

Who believed that the history of society was one of class struggle?

• Emile Durkheim
• Erving Goffmann
• George Herbert Mead

Who coined the phrase symbolic interactionism?

• Herbert Blumer
• Lester F. Ward
• W. I. Thomas

A symbolic interactionist may compare social interactions to:

• human organs
• theatrical roles

Which research technique would most likely be used by a symbolic interactionist?

• Participant observation
• Quantitative data analysis
• None of the above

1.4 Why Study Sociology?

Kenneth and Mamie Clark used sociological research to show that segregation was:

• of no importance

What did the Clarks use in their experiment noted in Exercise 1.13 ?

• children and dogs
• adults and dolls
• children and dolls
• adults and pets

Studying sociology helps people analyze data because they learn:

• interview techniques
• to apply statistics
• to generate theories
• all of the above

Berger describes sociologists as concerned with:

• monumental moments in people’s lives
• common everyday life events
• both a and b
• none of the above

Berger writes that sociology

• is not an academic discipline
• makes the strange familiar
• makes the familiar strange
• is not a science

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• Authors: Tonja R. Conerly, Kathleen Holmes, Asha Lal Tamang
• Publisher/website: OpenStax
• Book title: Introduction to Sociology 3e
• Publication date: Jun 3, 2021
• Location: Houston, Texas
• Book URL: https://openstax.org/books/introduction-sociology-3e/pages/1-introduction
• Section URL: https://openstax.org/books/introduction-sociology-3e/pages/1-section-quiz

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