In 1953, Mr. Molaison underwent surgery that removed two-thirds of his hippocampus—the part of the brain responsible for memory formation and storage—along with several other structures involved with emotions and memory, in an attempt to control his severe epilepsy.
The surgery successfully alleviated Mr. Molaison’s seizures. But it also left him without the ability to form new memories. Dr. Milner began working with him in 1955. In an interview from March 2010, she described her early experiences:
I gave him standard intelligence tests and memory tests . . . and I would talk to him, distract him and give him numbers to remember and so on. H.M. (Henry Molaison) could pay attention and had no problem with immediate memory, but as soon as he was distracted, he would forget what had happened before. So you could make this general prediction [about H.M.] that he’s going to forget everything, but no psychologist is happy with this sort of statement—you can’t test a null hypothesis. The challenge was: with practice, with repetition, could he learn something?
I went to the McGill psychology department and borrowed learning tasks to give him. I took down a maze task, which I was sure he wouldn’t learn, and he didn’t. It was a nice control test, because he showed absolutely no progress over three days. Then I gave him the mirror drawing task. H.M. did 30 trials over three days and at the end of the last trial, his performance was absolutely perfect. I can still remember him looking at what he had drawn, saying: “This is strange. I thought this would be difficult, but it looks as though I’ve done it rather well.” I was very excited because it showed that he could have this excellent performance without any awareness that the reason he was doing so well was that he had had the chance to practice the task over three days.
When I saw that H.M. had this beautiful learning of something he had no memory of having acquired, I then speculated that this task, which involved motor learning, depended on a different system in the brain. His surgeon had damaged his medial temporal system, but this was a kind of learning that was unaffected by this operation, so therefore it must involve other structures.
Following Mr. Molaison’s death in 2008, the Dana Foundation partially funded the dissection and digital preservation of his brain.
(Photo credit: Owen Egan; courtesy of the Montreal Neurological Institute, McGill University)