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  • On September 1st, 1953,

  • William Scoville used a hand crank and a cheap drill saw

  • to bore into a young man's skull, cutting away vital pieces of his brain

  • and sucking them out through a metal tube.

  • But this wasn't a scene from a horror film or a gruesome police report.

  • Dr. Scoville was one of the most renowned neurosurgeons of his time,

  • and the young man was Henry Molaison, the famous patient known as "H.M.",

  • whose case provided amazing insights into how our brains work.

  • As a boy, Henry had cracked his skull in an accident

  • and soon began having seizures, blacking out and losing control of bodily functions.

  • After enduring years of frequent episodes, and even dropping out of high school,

  • the desperate young man had turned to Dr. Scoville,

  • a daredevil known for risky surgeries.

  • Partial lobotomies had been used for decades to treat mental patients

  • based on the notion that mental functions were strictly localized

  • to corresponding brain areas.

  • Having successfully used them to reduce seizures in psychotics,

  • Scoville decided to remove H.M.'s hippocampus,

  • a part of the limbic system that was associated with emotion

  • but whose function was unknown.

  • At first glance, the operation had succeeded.

  • H.M.'s seizures virtually disappeared, with no change in personality,

  • and his IQ even improved.

  • But there was one problem: His memory was shot.

  • Besides losing most of his memories from the previous decade,

  • H.M. was unable to form new ones, forgetting what day it was,

  • repeating comments, and even eating multiple meals in a row.

  • When Scoville informed another expert, Wilder Penfield, of the results,

  • he sent a Ph.D student named Brenda Milner to study H.M. at his parents' home,

  • where he now spent his days doing odd chores,

  • and watching classic movies for the first time, over and over.

  • What she discovered through a series of tests and interviews

  • didn't just contribute greatly to the study of memory.

  • It redefined what memory even meant.

  • One of Milner's findings shed light on the obvious fact

  • that although H.M. couldn't form new memories, he still retained information

  • long enough from moment to moment to finish a sentence or find the bathroom.

  • When Milner gave him a random number,

  • he managed to remember it for fifteen minutes

  • by repeating it to himself constantly.

  • But only five minutes later, he forgot the test had even taken place.

  • Neuroscientists had though of memory as monolithic,

  • all of it essentially the same and stored throughout the brain.

  • Milner's results were not only the first clue for the now familiar distinction

  • between short-term and long-term memory,

  • but show that each uses different brain regions.

  • We now know that memory formation involves several steps.

  • After immediate sensory data is temporarily transcribed by neurons in the cortex,

  • it travels to the hippocampus,

  • where special proteins work to strengthen the cortical synaptic connections.

  • If the experience was strong enough,

  • or we recall it periodically in the first few days,

  • the hippocampus then transfers the memory back to the cortex for permanent storage.

  • H.M.'s mind could form the initial impressions,

  • but without a hippocampus to perform this memory consolidation,

  • they eroded, like messages scrawled in sand.

  • But this was not the only memory distinction Milner found.

  • In a now famous experiment, she asked H.M. to trace a third star

  • in the narrow space between the outlines of two concentric ones

  • while he could only see his paper and pencil through a mirror.

  • Like anyone else performing such an awkward task for the first time,

  • he did horribly.

  • But surprisingly, he improved over repeated trials,

  • even though he had no memory of previous attempts.

  • His unconscious motor centers remembered what the conscious mind had forgotten.

  • What Milner had discovered was that the declarative memory of names, dates and facts

  • is different from the procedural memory of riding a bicycle or signing your name.

  • And we now know that procedural memory

  • relies more on the basal ganglia and cerebellum,

  • structures that were intact in H.M.'s brain.

  • This distinction between "knowing that" and "knowing how"

  • has underpinned all memory research since.

  • H.M. died at the age of 82 after a mostly peaceful life in a nursing home.

  • Over the years, he had been examined by more than 100 neuroscientists,

  • making his the most studied mind in history.

  • Upon his death, his brain was preserved and scanned

  • before being cut into over 2000 individual slices

  • and photographed to form a digital map down to the level of individual neurons,

  • all in a live broadcast watched by 400,000 people.

  • Though H.M. spent most of his life forgetting things,

  • he and his contributions to our understanding of memory

  • will be remembered for generations to come.

On September 1st, 1953,

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B1 TED-Ed memory hippocampus brain young man distinction

【TED-Ed】What happens when you remove the hippocampus? - Sam Kean

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    稲葉白兎 posted on 2014/11/30
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