Researchers in the United Kingdom say they've found a way to study what produces déjà vu -- the feeling people get that they've seen or experienced something before.
Using hypnosis, a team at the University of Leeds says it can re-create the phenomenon to get a better understanding of what causes it.
"So far, we've completed the natural history side of this condition. We've found ways of testing for it and the right clinical questions to ask," Chris Moulin -- one of the researchers -- told the university's newspaper. "The next step is ... to find ways to reduce the problem."
Though most people experience déjà vu as a fleeting oddity that occurs rarely, there are those who live with it constantly -- a condition known as déjà vecu -- and it's hoped this new research will give scientists a way to treat them.
Haven't I Heard This Before?
When we see or experience something, our brain must first determine if it's something we've seen or experienced previously. If it has, it unlocks the associated memory in another part of the brain.
The team believes that déjà vu is caused by a disruption in those memory functions -- the brain triggers that "feeling" of memory, even though there isn't one there.
"The exciting thing about déjà vu is that it is the results of two opposing evaluations, the knowledge that something hasn't happened before but the feeling that it has," Moulin said in his blog. "We believe that one of the functions of the temporal lobe [a part of the brain located behind the ears] is to produce these feelings of memory. Sometimes, when this area is overactive, or 'tricked' into thinking something is familiar, we get a brief sensation of feeling something is old but knowing it is new."
But because déjà vu is usually a passing and unpredictable event, the team needed to devise a way to re-create the experience for study.
Eighteen subjects were shown a list of 24 words, and then they were hypnotized. While under the researchers' spell, the volunteers were told that when they woke up and were shown words surrounded by a red frame, they'd feel as if they'd seen them before but wouldn't know when.
Words shown in a green frame would appear as part of the original list.
Volunteers were then brought out of their trances and shown another list of 24 words. This time the list contained both words that had appeared on the original list and new ones, all framed in different colors including green and red.
Ten of the subjects in the experiment said they felt odd when they saw the new words and those in red boxes, and five of those volunteers said it felt like déjà vu.
For Some, Every Day Is Groundhog Day
For most of us, déjà vu doesn't have a negative impact on our lives and is not the most pressing medical issue we deal with.
But for those suffering from déjà vecu -- an almost constant feeling of déjà vu -- it can be debilitating.
"We are surprised by the common experience of these people: Nearly all have withdrawn from watching television, for instance, saying that they've seen each program (even if it is new) before," Moulin wrote. "They all seem to have difficulties for the most novel events in their life: If they go to a new place, they are likely to claim they've been there before."
Though Moulin acknowledges that there are lots of theories on déjà vu and there's significant evidence that it is linked to temporal lobe epilepsy -- epileptics often have strong feelings of déjà vu just before a seizure -- he says it is also a normal, healthy experience that shouldn't keep you up at night.
"If they [déjà vu experiences] occur alongside more serious forgetfulness or other difficulties, it is worth talking to your family doctor about them," he wrote. "But, just like momentary forgetfulness, forgetting someone's name, having a nightmare or having the hiccups, it isn't necessary to worry about them normally, or contact the doctor when you experience one."