HM’s case study is one of the most famous and important case studies in psychology, especially in cognitive psychology. It was the source of groundbreaking new knowledge on the role of the hippocampus in memory.
Background Info
“Localization of function in the brain” means that different parts of the brain have different functions. Researchers have discovered this from over 100 years of research into the ways the brain works. One such study was Milner’s case study on Henry Molaison.
The memory problems that HM experienced after the removal of his hippocampus provided new knowledge on the role of the hippocampus in memory formation (image: wikicommons)
At the time of the first study by Milner, HM was 29 years old. He was a mechanic who had suffered from minor epileptic seizures from when he was ten years old and began suffering severe seizures as a teenager. These may have been a result of a bike accident when he was nine. His seizures were getting worse in severity, which resulted in HM being unable to work. Treatment for his epilepsy had been unsuccessful, so at the age of 27 HM (and his family) agreed to undergo a radical surgery that would remove a part of his brain called the hippocampus. Previous research suggested that this could help reduce his seizures, but the impact it had on his memory was unexpected. The Doctor performing the radical surgery believed it was justified because of the seriousness of his seizures and the failures of other methods to treat them.
Methods and Results
In one regard, the surgery was successful as it resulted in HM experiencing less seizures. However, immediately after the surgery, the hospital staff and HM’s family noticed that he was suffering from anterograde amnesia (an inability to form new memories after the time of damage to the brain):
Here are some examples of his memory loss described in the case study:
- He could remember something if he concentrated on it, but if he broke his concentration it was lost.
- After the surgery the family moved houses. They stayed on the same street, but a few blocks away. The family noticed that HM as incapable of remembering the new address, but could remember the old one perfectly well. He could also not find his way home alone.
- He could not find objects around the house, even if they never changed locations and he had used them recently. His mother had to always show him where the lawnmower was in the garage.
- He would do the same jigsaw puzzles or read the same magazines every day, without ever apparently getting bored and realising he had read them before. (HM loved to do crossword puzzles and thought they helped him to remember words).
- He once ate lunch in front of Milner but 30 minutes later was unable to say what he had eaten, or remember even eating any lunch at all.
- When interviewed almost two years after the surgery in 1955, HM gave the date as 1953 and said his age was 27. He talked constantly about events from his childhood and could not remember details of his surgery.
Later testing also showed that he had suffered some partial retrograde amnesia (an inability to recall memories from before the time of damage to the brain). For instance, he could not remember that one of his favourite uncles passed away three years prior to his surgery or any of his time spent in hospital for his surgery. He could, however, remember some unimportant events that occurred just before his admission to the hospital.
Brenda Milner studied HM for almost 50 years – but he never remembered her.
Results continued…
His memories from events prior to 1950 (three years before his surgery), however, were fine. There was also no observable difference to his personality or to his intelligence. In fact, he scored 112 points on his IQ after the surgery, compared with 104 previously. The IQ test suggested that his ability in arithmetic had apparently improved. It seemed that the only behaviour that was affected by the removal of the hippocampus was his memory. HM was described as a kind and gentle person and this did not change after his surgery.
The Star Tracing Task
In a follow up study, Milner designed a task that would test whether or not HMs procedural memory had been affected by the surgery. He was to trace an outline of a star, but he could only see the mirrored reflection. He did this once a day over a period of a few days and Milner observed that he became faster and faster. Each time he performed the task he had no memory of ever having done it before, but his performance kept improving. This is further evidence for localization of function – the hippocampus must play a role in declarative (explicit) memory but not procedural (implicit) memory.
Cognitive psychologists have categorized memories into different types. HM’s study suggests that the hippocampus is essential for explicit (conscious) and declarative memory, but not implicit (unconscious) procedural memory.
Was his memory 100% gone? Another follow-up study
Interestingly, HM showed signs of being able to remember famous people who had only become famous after his surgery, like Lee Harvey Oswald (who assassinated JFK in 1963). (Image: wikicommons)
Another fascinating follow-up study was conducted by two researchers who wanted to see if HM had learned anything about celebrities that became famous after his surgery. At first they tested his knowledge of celebrities from before his surgery, and he knew these just as well as controls. They then showed him two names at a time, one a famous name (e.g. Liza Minelli, Lee Harvey Oswald) and the other was a name randomly taken from the phonebook. He was asked to choose the famous name and he was correct on a significant number of trials (i.e. the statistics tests suggest he wasn’t just guessing). Even more incredible was that he remembered some details about these people when asked why they were famous. For example, he could remember that Lee Harvey Oswald assassinated the president. One explanation given for the memory of these facts is that there was an emotional component. E.g. He liked these people, or the assassination was so violent, that he could remember a few details.
HM became a hugely important case study for neuro and cognitive Psychologists. He was interviewed and tested by over 100 psychologists during the 53 years after his operation. Directly after his surgery, he lived at home with his parents as he was unable to live independently. He moved to a nursing home in 1980 and stayed there until his death in 2008. HM donated his brain to science and it was sliced into 2,401 thin slices that will be scanned and published electronically.
Critical Thinking Considerations
- How does this case study demonstrate localization of function in the brain? (e.g.creating new long-term memories; procedural memories; storing and retrieving long term memories; intelligence; personality)(Application)
- What are the ethical considerations involved in this study? (Analysis)
- What are the strengths and limitations of this case study? (Evaluation)
- Why would ongoing studies of HM be important? (Think about memory, neuroplasticity and neurogenesis) (Analysis/Synthesis/Evaluation)
- How can findings from this case study be used to support and/or challenge the Multi-store Model of Memory? (Application/Synthesis/Evaluation)
Exam Tips
- This study can be used for the following topics:
- Localization – the role of the hippocampus in memory
- Techniques to study the brain – MRI has been used to find out the exact location and size of damage to HM’s brain
- Bio and cognitive approach research methods – case study
- Bio and cognitive approach ethical considerations – anonymity
- Emotion and cognition – the follow-up study on HM and memories of famous people could be used in an essay to support the idea that emotion affects memory
- Models of memory – the multi-store model: HM’s study provides evidence for the fact that our memories all aren’t formed and stored in one place but travel from store to store (because his transfer from STS to LTS was damaged – if it was all in one store this specific problem would not occur)
References
Milner, Brenda. Scoville, William Beecher. “Loss of Recent Memory after Bilateral Hippocampal Lesions”. The Journal of Neurology, Neurosurgery and Psychiatry. 1957; 20: 11 21. (Accessed from web.mit.edu)
The Man Who Couldn’t Remember”. NOVA Science Now. An interview with Brenda Corkin. 06.01.2009.
Here’s a good video recreation documentary of HM’s case study…
Travis Dixon is an IB Psychology teacher, author, workshop leader, examiner and IA moderator.