Brain mechanism explains sense of deja vu

By Julie Steenhuysen

CHICAGO (Reuters) - Most people have had deja vu -- that eerie sense of having experienced something before -- but U.S. researchers have identified the part of the brain responsible for this sensation, and they think it may lead to new treatments for memory-related problems.

They said neurons in a memory center of the brain called the hippocampus make a mental map of new places and experiences, then store them away for future use.

But when two experiences begin to seem very much alike, these mental maps overlap and start to blur.

"Deja vu occurs when this ability is challenged," said Susumu Tonegawa, a professor of biology and neuroscience at the Massachusetts Institute of Technology in Cambridge, whose work appears in the journal Science.

It is really just a malfunction in the brain's ability to sort through new information, something called episodic memory.

"This is very important for an intelligent animal like human beings so you know what's going on around you and you can recall it later," said Tonegawa in a telephone interview.

He and colleagues studied mice that were genetically altered to lack a gene in a specific part of the hippocampus called the dentate gyrus, which they found to be critical in forming the ability to sort through similar experiences.

Mice who lacked this ability were moved from one cage to a second, similar cage and then back to the first cage. In one cage, they got a mild electrical shock to the foot. In the other, they did not.