One of the most important figures in the history of brain research—and to me, as a former student of brain and behaviour, one of the most tragic and moving—died earlier this week at the age of 82. Henry Gustav Molaison, better known in the psychological literature as H.M., had a brain operation at the age of 27 to try to alleviate intractable seizures (the result of an accident at the age of 9). The surgery—cutting into the part of the brain called the hippocampus—successfully stopped the seizures, but came with a horrifying side-effect: Molaison could no longer form any long-term memories.
His short-term memory—e.g. remembering a phone number for the length of time needed to dial it—was unaffected, and everything he learned prior to his operation was retained, so he could cope reasonably well with day-to-day existence. However, H.M. never remembered experiencing anything or going anywhere a few seconds after doing it. Even when researchers met with him hundreds of times it was always as if he was meeting them for the first time. Every time he was told of his mother’s death his grief was as fresh as if he’d never been told.
From H.M. it was discovered by Brenda Milner of McGill University, that even though one kind of long-term memory is affected by hippocampal damage, another type of memory is not. H.M. could learn complex and difficult motor tasks (e.g. tracing a star while looking through a mirror); even though he never remembered doing the task, he got noticeably better at it over time. This “muscle memory” is why doing things learned long ago, like playing a once much-practised piece of music, or riding a bicycle, can be performed surprisingly well years later.
After working with hundreds of researchers over the years, H.M. had a vague idea that his story was somehow unusual, but he never could parse the details of why. He did thoroughly learn that he had a bad memory. His only life-lasting memories were ones that predated his 1953 operation, and they eventually lost any narrative thread or context in his existence. He remarked that his life was like constantly waking from a dream.
After his death H.M.’s brain was preserved for study, which will hopefully provide researchers with even more insights from a tragic life.
No comment yet
Laura says:
December 6, 2008 at 2:30 pm (UTC 0)
In a lovely article in the New Yorker, the neurologist Oliver Sacks describes the case of Clive Wearing, a musicologist who was stricken by a brain infection that effectively wiped out all of his memories, both pre- and post-illness. His entire existence was based on about 10 seconds of fluid memory, and he could forget that something happened, literally in a blink of an eye. Even though he had very little sense of who he was, he could converse entertainingly (if a bit repetitively), play and compose music with feeling and emotion, and—somehow—unconditionally love his wife and grown children, even though he didn’t always know their names or faces.