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April 7, 2014

A man with amnesia taught us how memories become personal

Kent Cochrane, the amnesiac known throughout the world of neuroscience and psychology as K.C., died last week at age 62 in his nursing home in Toronto, probably of a stroke or heart attack. Although not as celebrated as the late American amnesiac H.M., for my money K.C. taught us more important and poignant things about how memory works. He showed how we make memories personal and personally meaningful. He also had a heck of a life story.

During a wild and extended adolescence, K.C. jammed in rock bands, partied at Mardi Gras, played cards till all hours, and got into fights in bars; he was also knocked unconscious twice, once in a dune-buggy accident, once when a bale of hay conked him on the head. In October 1981, at age 30, he skidded off an exit ramp on his motorcycle. He spent a month in intensive care and lost, among other brain structures, both his hippocampuses.

As H.M.'s case demonstrated in the early 1950s, the hippocampus - you have one in each hemisphere of your brain - helps form and store new memories and retrieve old ones. Without a functioning hippocampus, names, dates and other information falls straight through the mind like a sieve. At least that's what supposed to happen. K.C. proved that that's not quite true - memories can sometimes bypass the hippocampus.

After the motorcycle accident, K.C. lost most of his past memories and could make almost no new memories. But a neuroscientist named Endel Tulving began studying K.C., and he determined that K.C. could remember certain things from his past life just fine. Oddly, though, everything K.C. remembered fell within one restricted category: It was all stuff you could look up in reference books, like the difference between stalactites and stalagmites or between spares and strikes in bowling. Tulving called these bare facts "semantic memories," memories devoid of all context and emotion.

At the same time K.C. had zero "episodic memory" - no memories of things he'd personally done or felt or seen. For instance, in 1979 K.C. surprised his family the night before his brother's wedding by getting a perm. For the rest of his life he knew his brother had gotten married and could recognize family members in the wedding album (the facts), but he didn't remember being at the wedding and had no idea how his family reacted to his curly hair (the personal experiences).

The little that K.C. did retain about his pre-accident life sounds like something he looked up in a particularly dry biography of himself. Even pivotal moments had been reduced to bullet points in an index. He knew his family had to abandon his childhood home because a train derailed and spilled toxic chemicals nearby; he knew a beloved brother died two years before his own accident. But these events had no emotional import anymore. They were just stuff that happened.

This work, along with studies of similar patients, provided strong evidence that our episodic and semantic memories rely on different brain circuits. The hippocampus helps record both types of memories initially, and it helps retain them for the medium term. The hippocampus also helps us access old personal memories in long-term storage in other parts of the brain. But to access old semantic memories, the brain seems to use the parahippocampus, an extension of the hippocampus on the brain's southernmost surface. K.C., whose parahippocampuses survived, could therefore remember to sink the eight ball last in pool (semantic knowledge), even though every last memory of playing pool with his buddies had disappeared (personal knowledge).

What's more, while a healthy hippocampus usually records new semantic, factual memories, the parahippocampus can - albeit excruciatingly slowly - absorb new facts if it has to. For instance, after years of shelving books as a volunteer at a local library, K.C.'s parahippocampus learned the Dewey decimal system, even though he had no idea why he knew it.

Scientists later realized that H.M., who also had a healthy parahippocampus, had similarly picked up a few choice facts after the 1953 surgery that destroyed his hippocampuses. H.M. loved doing crossword puzzles, and after seeing the clue a thousand times, he dimly recalled that "Salk vaccine target" equaled P-O-L-I-O. And through incessant references, H.M. retained a sliver of information about the 1969 moon landing and 1963 Kennedy assassination. Unlike all the people who, according to the cliché, knew exactly where they were when they learned those things, H.M. didn't - that's episodic memory. But he retained the basic fact.

In general, all memories are probably stored as personal memories initially: You might have first learned that Abraham Lincoln was the 16th president while on a field trip to Washington or more likely when you got that item wrong on a quiz and it got seared into your brain. After that, however, the memory gradually shifted to become semantic, and you retained only the more abstract knowledge that Abe = 16.

Still, there's one thing K.C. never lost - his sense of self, his sense of who he was deep down. He knew his own personality traits and knew where he came from. Knew his likes and dislikes and what he looked like in the mirror. Kent Cochrane always knew he was Kent Cochrane - not even severe trauma could take that away from him.

That's actually a common theme in the neuroscience of accidents. It's easy to see the victims of brain damage as reduced or diminished, and they are in some ways. But much of what they feel from moment to moment is exactly what you or I feel, and there's almost nothing short of death that can make you forget who you are. Amid all the fascinating injuries in neuroscience history, you'll come across a lot of tales of woe and heartbreak. But there's an amazing amount of resiliency in the brain, too.

 

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