H.M., whose full name has now been revealed as Henry Gustav Molaison, lost completely the ability to form new memories following a radical surgical procedure to treat his severe and intractable epilepsy.
The operation was performed in 1953 by William Scoville, a neurosurgeon at Hartford Hospital in Connecticut. Using an experimental technique he had recently developed, Scoville removed both of H.M.’s hippocampi in their entirety, together with some of the surrounding structures.
This cured H.M.’s epilepsy, but had severe effects on his memory: he was left with profound anterograde and retrograde amnesia. As well as being unable to form new memories, he also could not remember anything that had happened to him in the 10 years or so before his operation.
Following the surgery, H.M.’s memory deficit was studied intensively. He was the subject of several groundbreaking studies by psychologist Brenda Milner of McGill University, and the more recent studies by neuroscientist Suzanne Corkin of MIT were ongoing when he died earlier this week.
H.M.’s amnesia was so severe that he never recognized Milner, despite working with her for more than 50 years. “He was a very gracious man, very patient, always willing to try these tasks,” Milner said in a recent interview, “and yet every time I walked in the room, it was like we’d never met.”
Milner’s early studies of H.M. showed that the hippocampus is critical for memory formation, and the subsequent finding that he could learn simple motor skills showed that there were at least two distinct memory mechanisms. Although H.M. left no survivors, his legacy will not be forgotten, because he has probably contributed more to our understanding of memory than any other individual.
Update: The San Diego Union Tribune reports that H.M.’s brain is to be taken to the Brain Observatory at UCSD, where it will be “sliced, stained and preserved in approximately 3,000 oversized glass slides”.