Brain Mechanism Explains
Sense Of Deja Vu
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
The mutant mice associated both cages with danger and began to
freeze when placed in either cage -- they could not determine
in which cage they got shocked.
Healthy mice quickly learned the difference and only froze in
the dangerous cage.
When the researchers tested the animals' brain activity,
the mutant mice reacted similarly in both cages, but the brain
activity of the healthy mice was different in each.
Tonegawa said the type of memory that allows people to quickly
distinguish different faces and places fades with age.
"Since we know the molecular and cellular pathway based
on our results, there is a possibility to use those molecular
targets to develop a drug to improve this connection," he
That is especially the case for neurodegenerative diseases like
He said the study settles 35 years of debate over how the brain
can distinguish between similar places and experiences.
"One big question about the memory is now taken care of,"
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