The Brain: The Flavor Of Memories

Emotions turn out to be key in how we remember--and can help us recast traumas dredged from the past

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    Second, even as it's kick-starting the body, the amygdala sends out a crackle of signals to the rest of the brain. Some of them put the senses on high alert, ready to deal with a threat. But these signals also tell the neurons that any memories recorded in the next few minutes need to be especially robust. One piece of evidence for this scenario: Lawrence Cahill, a colleague of McGaugh's at Irvine, showed subjects emotionally arousing film clips, simultaneously gauging the activity of their amygdalae using positron-emission tomography (PET) scans. Three weeks later, he gave the subjects a surprise memory quiz. The amount of amygdala activity predicted with great accuracy how well they remembered the film clips.

    Imaging studies also make clear that it isn't just dangers or tragic events that cement memory formation. Positive emotions, which are also mediated through the amygdala, have the same effect. Again, that's a perfectly reasonable evolutionary development. If eating or having sex makes you happy, you'll remember that and do it again, keeping yourself healthy and passing on your genes as well.

    This is an oversimplification, of course. Other neurotransmitters, and even plain glucose--the sugar the brain uses for energy--may also play a part. And then there's the peculiar case of a woman who contacted McGaugh because she remembers absolutely everything. The stress-hormone model does not appear to apply in her case. Says McGaugh: "At one point I asked if she knew who Bing Crosby was. She's 40, so Bing Crosby doesn't loom large in her life, but she knew he died on a golf course in Spain, and she gave me the date, just like that." Imaging researchers are working to determine whether the woman's brain is structurally different from everyone else's.

    But aside from such odd cases, virtually no expert doubts the connection between the hormones of emotion and memory--and nobody doubts that memory can be enhanced artificially. It's not necessarily a good idea, though. Give someone a shot of adrenaline, and memory temporarily improves. But it also drives up the heart rate, so it could be dangerous for the elderly. Other memory enhancers, like Ritalin or amphetamines, used by college students to cram for exams, are highly addictive. And some of the experimental drugs McGaugh is testing in rats can cause seizures. Unfortunately, he says, for people with truly serious memory problems, "existing drugs are not yet powerful enough or nice enough."

    For people haunted consciously or unconsciously by painful memories, there may be hope. Roger Pitman, a professor of psychiatry at Harvard medical school, is working to understand post-traumatic stress disorder (PTSD). The syndrome, he believes, is the result of brain chemicals reinforcing themselves in a cerebral vicious circle. "In the aftermath of a traumatic event," he says, "you tend to think more about it, and the more you think about it, the more likely you are to release further stress hormones, and the more likely they are to act to make the memory of that event even stronger."

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