Neuroscience's famed patient dies

Written byJennifer Evans

| 3 min read

Henry Molaison (HM), a patient with amnesia who helped scientists to unlock the secrets to how the brain processes learning and memory, died last week at the age of 82. HM participated in thousands of memory studies over the past 50 years, after a surgery to cure his debilitating epilepsy in the early 1950s altered his ability to form new memories. "[HM] was an extremely cooperative and gentle human being," linkurl:Brenda Milner,;http://www.mcgill.ca/about/history/pioneers/milner/ a neuropsychologist from the Montreal Neurological Institute and McGill University who studied HM for decades, told The Scientist. "He wanted to do something for science." HM's surgery involved removing sections of the right and left temporal lobe of the brain, fractioning the hippocampus. The procedure cured HM's seizures, but had an unintended consequence: although his intelligence was not affected, from 1953 onward new people, places and events slipped from his memory within a matter of seconds. Milner began traveling from Montreal to Hartford to work with HM, exposing him to series of memory tasks. At the time when Milner began working with HM the consensus among scientists was that memory was not isolated to a single region of the brain. "There was no CT scan, no fancy imaging equipment," to peer into the brain, Milner said, leaving researchers to rely on clinical observations. HM could remember his childhood, his epilepsy, and even that he had a major surgery, but if Milner left the room, upon her return it was as if HM was meeting her for the very first time, Milner said. "From that moment on, you are stuck while the lives of others around you progress," she said of his condition. Early tests showed HM's working memory, or his ability to remember short sequences of numbers or words for around 30 seconds, was preserved, suggesting the hippocampus was not required for working memory but in the transfer of short-term to long-term memories. In 1962, Milner discovered that not all of HM's long-term memories were destroyed when she had him do a drawing task to test his motor memory. Milner instructed HM to trace within the double lines of a five-point star, using only a mirror's reflection for guidance -- a challenging task that becomes easier with practice, Milner said. HM repeated the drawing task several times per day, each time believing it was the first. Each day he performed the task, he started off better than the day before, eventually perfecting it. "He was so proud of himself," Milner said, of HM's perfect performance. "He turned to me and said 'I thought this would be difficult.' It was an amazing dissociation of motor learning and loss of memory." The findings revealed to scientists there were at least two memory systems working through different networks in the brain -- declarative memory, which allows the storage of new people and places and implicit, or subconscious memory, like motor memory, which allows a person to ride a bike after several years off. In the decades since the breakthrough, scientists continued to work with HM to improve their understanding of the memory systems. Even late into the night on Tuesday (Dec. 2), just hours after HM's death, MIT researchers took MRI scans of HM's brain to help identify the full extent of HM's temporal damage, the linkurl:The New York Times;http://www.nytimes.com/2008/12/05/us/05hm.html reported. Beginning next month, researchers at the Brian Observatory at the University of California at San Diego will begin sectioning HM's brain, using imaging techniques to probe even deeper into the brain of the famed amnesiac, linkurl:The San Diego Union-Tribune;http://www.signonsandiego.com/news/metro/20081206-9999-1n6brain.html reported. "I am very indebted to him," Milner said. "I constantly felt like it was such a shame we couldn't reward him" because he couldn't remember from moment to moment. "I would've liked to do something for someone whose done so much" for science.
**__Related stories:__***linkurl:My healthy old brain;http://www.the-scientist.com/news/display/55174/
[7th November 2008]*linkurl:Making mice forget;http://www.the-scientist.com/blog/display/55102/
[22nd October 2008]*linkurl:Exceptional memories;http://www.the-scientist.com/article/display/20950/
[16th December 2002]

Neuroscience's famed patient dies

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