An operation meant to stop his seizures took away his ability to form new memories for the rest of his life. Henry Molaison lived another fifty-five years, and what researchers learned from him rewrote the psychology of memory.
📚 What you need to know
The brain has two hemispheres, covered by a thin layer called the cerebral cortex.
It has four main lobes: frontal, parietal, occipital and temporal. Each is divided between the hemispheres, so each lobe mirrors itself on the other side.
Cognitive neuroscience is the scientific study of brain structure and function and how they relate to behaviour.
It is central to localisation of function — mapping which structures are linked to which behaviours.
Damage to a structure impairs the function tied to it. Damage to Broca’s area disrupts fluent speech; damage to the pre-frontal cortex can change personality.
Anterograde amnesia is the inability to form new memories. Retrograde amnesia is the loss of memories from before the damage.
The study you need is Milner (1958) and Scoville (1997), the case of HM.
Key study: the case of HM
Part of the study
What happened
Aim
To investigate memory loss in a brain-damaged patient known as HM, through examination of his brain post-mortem and via MRI.
Participant
HM (Henry Molaison) was knocked down by a bicycle at nine and began having epileptic seizures. At 27 he underwent a bilateral medial temporal lobe resection, which removed roughly two thirds of his hippocampus. His epilepsy improved, but he was left with severe anterograde amnesia and partial retrograde amnesia.
Procedure
Brenda Milner visited him frequently and ran a wide range of tests and measures: personality and mood tests, depression questionnaires and interviews with psychiatrists. His scores showed no depression, anxiety or psychosis, and he was aware of his own condition. His IQ was normal, but the Wechsler Memory Scale showed severe impairment. MRI scans in 1992 and 1993 confirmed the medial temporal lobe had been particularly affected. Milner and Corkin studied him for over 50 years, until his death at 82.
Milner’s observations
He frequently forgot what had happened that day, thought he was younger than he was, forgot the names of people he had just met, and said every day felt like waking from a dream.
Results
Memory is not simply one of a bundle of cognitive functions sitting in the cortex. It is a distinct function, localised to the temporal lobe and specifically the hippocampus.
Conclusion
Hippocampal damage may be linked to long-term anterograde amnesia, and the formation of new memories is tied to the hippocampus. This supports localisation of function.
The split is the whole finding. If memory were just part of general intelligence, damaging it should have damaged everything else too.
The normal IQ result is the detail that makes this case famous. It proves memory can be knocked out while the rest of thinking stays intact — which is exactly what localisation of function predicts.
Evaluating the research
What is strong about it
The case study used both qualitative and quantitative methods, generating data that was both reliable and genuinely explanatory.
It was groundbreaking, giving enormous insight into localised regions of the brain at a time when very little was known.
He was studied for over 50 years, which is an extraordinary depth of longitudinal data.
What is weaker about it
A possible confounding variable is that HM’s brain may already have been damaged by years of epilepsy, which reduces the validity of attributing everything to the surgery.
Not enough is known about the brain to draw iron-clad conclusions about exactly which functions are hit by which damage.
It is a single case, so generalising from it is risky.
Link to concepts
Bias: case studies involve researchers working closely with one participant over a long period, which risks researcher bias affecting objectivity. Getting too close can lead to over-reporting some findings and under-reporting others, perhaps from a sense of duty towards the participant. Researchers should practise reflexivity throughout to keep the results credible.
Responsibility: HM was a vulnerable person with no recollection of recent events — he did not even recognise the researchers — and lived under supervision. Informed consent is the central problem: how can someone consent to something they will instantly forget? His mother initially gave consent by proxy, followed by a court-appointed conservator after her death. His family later contested this, arguing he never willingly agreed to be studied.
EXAM PRACTICE
Discuss the effect of brain damage on one cognitive process. [22]
Step 1: set up localisation
Cognitive neuroscience maps structures to functions; damage to a structure should impair the function tied to it.
Step 2: the case
HM. Bilateral medial temporal lobe resection at age 27 removed about two thirds of the hippocampus.
Step 3: the pattern of loss
Severe anterograde amnesia, partial retrograde amnesia, but normal IQ and poor Wechsler Memory Scale scores.
Step 4: what it shows
Memory is a distinct function localised to the hippocampus, not a by-product of general cognition.
Step 5: evaluate
Rich mixed-methods data over 50 years, but a single case, a possible epilepsy confound, researcher bias, and serious consent problems.
Localisation + case + pattern + conclusion + evaluationThe normal IQ alongside impaired memory is the sentence that earns the analysis mark.
💡 Exam tip
Define anterograde and retrograde separately. HM had both, in different degrees.
Name the operation properly: bilateral medial temporal lobe resection.
Consent by proxy is precise ethics vocabulary and worth a mark.
Use HM again on the multi-store model page — he supports separate memory stores.
Say case study and note that generalisability is limited by design, not by carelessness.
⚠ Common mix-up
Saying HM lost all his memories. Older long-term memories stayed reasonably intact.
Swapping anterograde and retrograde. Anterograde looks forward: no new memories.
Saying the whole hippocampus was removed. It was about two thirds, on both sides.
Claiming HM had low intelligence. His IQ was normal.
Calling it an experiment. It is a longitudinal case study; nothing was manipulated.
Up next: Atkinson and Shiffrin’s Multi-Store Model — the first serious attempt to draw memory as a diagram, and the evidence that made it look right.
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