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Paging Dr. Gupta

Haven't I seen this story before?

Researchers hope study of déjà vu will help understand memory

By A. Chris Gajilan
CNN

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PAGING DR. GUPTA

YOUR E-MAIL ALERTS

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Memory

(CNN) -- "I know I've been here before."

"This seems so familiar."

"I think I've dreamt that we were in exactly this same situation."

Most of us have been struck by that uncanny feeling that you've been in a room, place or situation before ... but you know you haven't.

It's called "déjà vu." The literal translation from French is "already seen."

"Déjà vu is in essence an illusion of familiarity except that it's a very intense illusion," according to psychologist Alan Brown of Southern Methodist University.

Déjà vu research, which goes back to the early 1900s, has focused on the supernatural -- from reincarnation to the presence of the paranormal.

But researchers at Southern Methodist and Duke universities say such explanations are unlikely. They are trying to take a more quantitative approach to the nebulous subject.

"The amount of scientific credibility might surprise people," says Brown, who for years has been studying the phenomenon of déjà vu and the people who experience it.

Brown and his fellow researchers realize that déjà vu still seems to be shrouded in a great deal of mystery. By understanding déjà vu better, they hope to better understand the biology of memory.

Brown has recorded hundreds of accounts of déjà vu and analyzed surveys on the subject. According to his estimates, two-thirds of all people experience it at some time or another. He's also uncovered details on who is more likely to feel the sudden flashbacks.

"Déjà vu tends to peak around the late teens and early 20s and then tapers off," Brown says. He adds that it tends to happen two or three times a year among younger adults, decreasing to once a year in midlife and with older adults, perhaps as seldom as once every four or five years.

What else increases your odds? If you have a higher level of education or income. If you're liberal rather than conservative. If you travel. If you've had it once, you're likely to have it again.

Déjà vu tends to occur more frequently when you're in the company of friends, when you're relaxing, when you're in familiar circumstances and when you're indoors. It also tends to happen at the end of the day and towards the end of the week.

"There are a lot of different ways we can have that experience. Sort of like there are a number of different ways you can have a stomachache," according to Brown.

One explanation may come from a small group of epileptics who experience déjà vu immediately before a seizure. Scientists have traced the seizures to the brain's frontal lobe -- the area responsible for familiarity. It may be irregular activity in that part of the brain causing déjà vu for more than just those afflicted with temporal lobe epilepsy.

Another theory involves the multiple pathways that bring information from the sensory organs to the brain. Usually the signals travel at the same rate -- to the millisecond, but sometimes they may be out of synch.

Brown hypothesizes, "Occasionally, one of the paths may have a neurological event occur where it slows it down slightly." That near negligible gap can cause you to think you've felt something before ... and you have, but just milliseconds before.

Another approach is called implicit memory interpretation. That strange, overwhelming feeling of inexplicable familiarity when you walk into a room may be caused a small, unexpected detail. For example, you may not realize that this room you walked into has a lamp that is identical to the one that was in your grandmother's living room when you were four years old. That small lamp, not the entire situation, has triggered déjà vu.

It's not always an object, but sometimes scents or sounds, Brown says.

Another example of a subconscious trigger involves your experience while you're not fully aware. For example, you could be seeing something while talking on a cell phone. When you're looking at something but not paying attention to it, you are still taking in information from your surroundings. You may see those same items again and feel déjà vu. In fact, you have experienced it before, but you weren't paying full attention.

"Our information does get in often under our radar and it implants itself and we react later in ways that surprise us," says Brown.

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