Molaison was only one of a very few patients who had a radical operation that removed inner sections of both temporal lobes to cure otherwise untreatable temporal lobe epilepsy.
At the time, it wasn’t known that removing the hippocampus on both sides of the brain would lead to a profound amnesia that left the patient with the inability to create new ‘declarative’ memories – ones that can be recalled into the conscious mind.
The procedure was only carried out on a handful of patients before the profound effects became clear. The neurosurgeon William Scoville later campaigned against its use.
The rest, as they say, is history and owing to Molaison’s cheerful participation in numerous memory experiments we know a great deal more about the neural basis of memory. Hopefully the new high resolution digitised brain slices will allow a fine detail look at the relationship between HM’s brain and his abilities.
You’ll not find a better account of the project, so do head over and check out the Neurophilosophy piece.
My only slight addendum would be that the distinction between short and long-term memory was not initially drawn from HM. This distinction was originally made by ‘father of psychology’ William James who described it as ‘primary’ and ‘secondary’ memory in his 1890 book Principles of Psychology.
However, because HM had intact short-term memory (for example, he could repeat telephone numbers back to himself) but was not able to store anything effectively in long-term memory, he gave the first clues that this distinction was reflected in the structure of the brain.
This was all but confirmed in 1970 when neuropsychologists Tim Shallice and Elizabeth Warrington reported on Patient KF who had the reverse pattern of impairment – no short term memory, but with with normal long-term memory.
This showed that each of the two forms of memory could be independently impaired after brain damage and so almost certainly depend on distinguishable brain systems.