Brain Scans Show How Memories Are Retrieved

'Mental time travel' takes you back to creation of a memory, researcher says

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By Ed Edelson
HealthDay Reporter

THURSDAY, Dec. 29, 2005 (HealthDay News) -- Remember the last vacation you took?

That question can release a flood of memories -- where you went, how you got there, the things you did while on the beach or the ski slope, and more.

And now neuroscientists at Princeton University have discovered the mechanism of this "mental time travel," a finding that may someday help people with memory problems of the sort that occur in Alzheimer's disease.

"Our goal is to really figure out what is going on in the brain when you think back to past events," said Kenneth A. Norman, an assistant professor of psychology at Princeton and lead author of the report in the Dec. 23 issue of Science.

A series of brain scans done with the help of nine volunteers showed that "what you are trying to do when you remember is to recapture your mental state in the original experience," Norman said. "You try to make your mindset as much as possible what it was at that event."

Norman and his colleagues -- Sean M. Polyn, one of them, earned his doctorate doing the study -- had the volunteers look at three sets of pictures, of famous faces, famous locations and common objects. While they did that, a computerized program recorded the pattern of brain activity.

"The program figured out what does this particular person's brain look like when it thinks about objects, faces, locations," Norman explained.

When the volunteers were asked to recall specific items, the computer program showed that their brain states gradually aligned with the brain states they showed when they first studied the pictures.

More than that, second-by-second scans enabled the researchers to predict the kind of item that a volunteer would think of next.

This would seem to be a mind reader's delight (wouldn't you like to know what silent thoughts that person across the table from you is really thinking), but Norman and his follow researchers have more serious goals.

"This gives us a new tool for understanding how normal people reconstruct memories," Norman said. "The better we understand how that works when it is successful, the better we will be able to understand what is going wrong in people where the process is not successful."

Norman is continuing work along that line, with the help of Jonathan Cohen, director of Princeton's Center for the Study of Brain, Mind and Behavior, and Vaidehi Natu, a researcher in his lab.

"The most important thing we have learned is that what you get out of memory is strongly influenced by the things around you -- when you run across an old object, remember a place," he said. "We hope to understand that information people are using to jar loose memories."

More information

To learn more about memory, visit the National Library of Medicine.

SOURCES: Kenneth A. Norman, Ph.D, assistant professor, psychology, Princeton University, Princeton, N.J.; Dec. 23, 2005, Science

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