Memory Is Mental Time Travel

Mind Recreates Past Reality When Remembering

Medically Reviewed by Louise Chang, MD on December 22, 2005
From the WebMD Archives

Dec. 21, 2005 -- When we try to remember something, we do mental time travel.

New studies show that as we try to recall something, our brain works to match the brain state we had during the event we are remembering. When our reassembled brain state is a close enough match to the old one, voila! We remember.

The finding comes from brain imaging studies by University of Pennsylvania postdoctoral student Sean Polyn, PhD, and colleagues.

"Memory retrieval is like revisiting the past," Polyn says, in a news release. "Brain patterns that are long gone can be revived by the memory system."

The findings appear in the Dec. 23 issue of Science.

Remembering Celebrities, Landmarks, and Things

Polyn's team asked volunteers to study three lists. Each list contained 30 items: celebrity photographs, pictures of famous places, and photos of common objects.

The brain stores different classes of things -- such as faces, places, and things -- in different ways. As each volunteer studied each item, the researchers scanned their brains with an fMRI (functional magnetic resonance imaging) device. This imaging lets researchers see which parts of the brain are being used, and when.

Later, the volunteers tried to remember the faces, places, and things in any order they liked while the researchers scanned their brains. Sure enough, as they tried to remember something, their brains began to look just as they did when they were learning that class of object.

And just before they reported the object they remembered, their brain activity matched the brain activity for that class of object.

"As subjects search for memories from a particular event, their brain state progressively comes to resemble their brain state during the sought-after event," Polyn and colleagues write. "And the degree of match predicts what kind of information the subjects will retrieve."

Polyn says the findings help explain a common experience.

"[It is] much like when you try to remember where you put your keys last night," Polyn says. "If you recall that you were washing dishes, that might trigger associated memories, leading you to remember that your keys are next to the sink."

And the findings also carry some hint of mind reading. The brain scans told the researchers -- before the subjects did -- what class of object the subjects were remembering.

Show Sources

SOURCES: Polyn, S.M. Science, Dec. 23, 2005; vol 310: pp 1963-1965. News release, University of Pennsylvania.
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