Case studies of brain-damaged patients: HM

HM's story

Henry Molaison had severe epilepsy for many years. In 1953, aged 27, the neurosurgeon William Beecher Scoville removed tissue from the medial temporal lobes of both hemispheres, including most of the hippocampus on each side. The seizures became much less frequent, but HM was left with severe amnesia.

He was studied for more than five decades, first by Brenda Milner and later by Suzanne Corkin's team at MIT. He was known publicly only as HM until his death in 2008, aged 82. After his death his brain was cut into 2,401 thin sections, which were digitised (Annese et al., 2014).

What his memory showed

• Anterograde amnesia: he could not form new conscious long-term memories (new words, faces, events).
• Some retrograde amnesia for the years before surgery.
• STM was normal: he could hold a conversation or a number briefly, but it was lost once his attention moved.
• He could still learn motor skills such as mirror drawing and got faster with practice, without remembering having practised (procedural memory).

Conclusions: the hippocampus is essential for transferring new information into LTM; STM and LTM are separate (supporting the multi-store model); and LTM has separate systems (procedural memory was spared).

Evaluating case studies

Strengths: rich, detailed, long-term data (high validity); rare cases allow study of things that could never be created ethically; they can challenge theories (KF challenged the single STM store).

Weaknesses: unique cases cannot be generalised; no control over the damage, and there is no 'before' baseline, so cause and effect are hard to establish; difficult to replicate; researchers may become too involved and biased; HM's earlier epilepsy and medication may also have affected his memory.

Ethics: people with amnesia cannot easily give informed consent or remember agreeing (consent from relatives or guardians is needed); confidentiality (initials only); protecting a vulnerable person from distress and over-testing (access to HM was restricted).

Worked example

Explain how the case of HM supports the multi-store model.

1. HM's STM was intact: he could hold information briefly.
2. He could not transfer new information into LTM after hippocampal damage.
3. So STM and LTM must be separate stores, with the hippocampus involved in transfer.

Answer: Intact STM but no new LTM shows the two stores are separate, as the model claims.

Check yourself

1. Which brain structure, essential for forming new long-term memories, was largely removed in HM's surgery?
   • Cerebellum
   • Occipital lobe
   • Frontal lobe
   • Hippocampus
   Show answer

   Hippocampus. Most of the hippocampus on both sides was removed.

2. HM could not form new long-term memories after his operation. This is
   • retrograde amnesia
   • anterograde amnesia
   • semantic dementia
   • a Type I error
   Show answer

   anterograde amnesia. Anterograde amnesia affects memories after the damage.

3. HM got better at mirror drawing with practice but could not remember practising. What does this show?
   • His short-term memory was destroyed
   • The working memory model is wrong
   • He was faking his amnesia
   • Procedural memory can work separately from conscious (declarative) memory
   Show answer

   Procedural memory can work separately from conscious (declarative) memory. Skill learning survived while conscious memory did not.

4. HM had surgery in 1953 aged 27 and died in 2008. How many years did he live after the operation?
   Show answer

   55 years. 2008 - 1953 = 55 years.

5. What is the main weakness of using HM's case to understand normal memory?
   • There is too little data about him
   • He was tested for only one day
   • He is one unique individual, so findings may not generalise to everyone
   • He was a volunteer sample
   Show answer

   He is one unique individual, so findings may not generalise to everyone. Single unusual cases may not represent normal brains.

6. Explain one ethical issue in studying patients such as HM.
   Show answer

   Patients with amnesia may not be able to give fully informed consent or remember agreeing, so researchers must get consent from relatives or guardians and protect them from distress.. Consent, confidentiality and protection of a vulnerable person are the main issues.

Practise with instant feedback Print this lesson

Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification (issue January 2026)
• Pearson International A Level Psychology component guide: WPS01
• Schmolck, Kensinger, Corkin and Squire (2002) Hippocampus 12 (full text)
• Simply Psychology: Multi-store memory model
• IAL Psychology revision site: Case studies: H.M.

Last updated 8 November 2026. Spotted a mistake? Tell us.