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Why Can Some People Recall Every Day Of Their Lives? Brain Scans Offer Clues

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Six years ago, we told you about a woman, identified as A.J., who could remember the details of nearly every day of her life. At the time, researchers thought she was unique. But since then, a handful of such individuals have been identified. And now, researchers are trying to understand how their extraordinary memories work.

Bob Petrella, 62, of Los Angeles had to go through a lot of memory testing to qualify as someone with superior autobiographical memory. First, there were lots of questions about news events from the past several decades, like the O.J. Simpson car chase.

Petrella scored 55 percent correct on the news events, according to a paper published in July in the journal Neurobiology of Learning and Memory. (Most people get 15 percent.) Then he was quizzed about his own life.

"They asked, 'What day of the week was Jan. 1, 1984?' — which was a Sunday," Petrella recalls. "And the Steelers, my favorite team, lost to the Raiders that day, 38-10."

Petrella is one of 11 individuals who have now been extensively studied by memory researcher James McGaugh at the University of California, Irvine. The testing has shown that Petrella and the others like him don't use memory tricks.

They don't have photographic memories. They're not savants. Other than their remarkable memories, they're normal, says McGaugh.

"They're reasonably successful in what they do. There is a professional violinist; there is Marilu Henner, who is a successful actress ... and so on," McGaugh says.

Surprisingly, Petrella and the group didn't do any better than you or I would on most standard memory tests — like repeating back lists of words, or a string of numbers. It's their autobiographical memory that's exceptional. Other types of memory are pretty much normal.

"People like us, we forget normal things. Like, I forgot where I parked my car a couple of months ago coming out of a theater. Or I forget where I left my keys," he says.

The researchers have identified another surprising set of behaviors that these individuals share.

"Most, if not all of them, have some obsessive-compulsive tendencies," says Petrella. "They tend to save a lot of objects. They tend to have some repetitive habits. They tend to store things."

Take Petrella, for example.

"He's germ-avoidant. If he drops his keys, he has to wash them. He can't wear shoes that have shoestrings, because shoestrings touch the ground," McGaugh says.

But the obsessive tendencies don't seem to interfere with daily living, McGaugh says. It's a tantalizing clue, especially when coupled with the MRI findings that a brain area known to be involved in obsessive-compulsive disorder, or OCD, is larger than normal in these folks.

This brain area, called the caudate, may be related to having the constant, repetitive and precise replay of past events. The brain scans also revealed other differences in brain structure.

"What we've identified are nine regions of the brains of these subjects that differ from those of control subjects," he said.

Many of these regions are involved in memory encoding and retrieval. McGaugh hopes further research on these individuals will reveal how their phenomenal memories work, and perhaps how ordinary memory works as well.

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.

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