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Scoville and Milner (1957) with a side of Corkin et al. (1997)

Scoville and Milner (1957)

Damage to the hippocampus and amnesia

  • Scoville and Milner (1957) described the case of H.M. who fell off his bicycle when he was 7 years old, injuring his head. He began to have epileptic seizures when he was 10. By the age of 27 the epileptic attacks prevented him from living a normal life.
  • Scoville performed an experimental surgery on H.M.’s brain to stop the seizures.  Specifically he removed parts of HM’s temporal lobes (part of his hippocampus along with it).The seizures stopped but H.M. suffered from amnesia for the rest of his life.
  • The case study of H.M. provides information on how particular brain areas and networks are involved in memory processing. This helped scientists to formulate new theories about memory functioning.

H.M.’s memory:

  • H.M. could no longer store new memories (anterograde amnesia). Most of his memories from before the operation remained intact (partial retrograde amnesia).
  • He could not transfer new semantic and episodic memories (explicit memories) into LTM.
  • He could form new long-term procedural memories (implicit memories).
  • He was able to carry on normal conversations (i.e. had some capacity for working memory) but he would forget what the conversation was about immediately.

Things we learned from HM:

  • The hippocampus play a critical role in converting memories of experiences from STM to LTM (the permanent store).
  • H.M. was able to retain some memories for events that happened long before his surgery. This indicates that the medial temporal region with the hippocampus is not the site of permanent storage in itself. It rather seems to play a role in how memories are organized and then stored elsewhere in the brain.
  • The fact that H.M. and other people with amnesia have deficits in some types of memories but not in others is taken as evidence that the brain has multiple memory systems that are supported by distinct brain regions.

Corkin et al. (1997)

On a side note: Corkin et al. (1997) used MRI to study H.M.’s lesion in the first attempt to use modern technology to study his brain.

The results of the MRI scan confirmed a relationship between damage to the medial temporal lobes (including the hippocampus) and H.M.’s amnesia. Although a tiny part of the hippocampus remained it was not enough to support normal memory function