Saturday, 16 June 2012

What is deja-vu?


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“It’s strange, I have the feeling I’ve already experienced this exact same situation”. The illusion of déjà-vu has been felt by many of us at least once in our lives. Where does this curious phenomenon come from? Here is a closer look at this strange feeling, with a few neurologists who are specialists in memory.

Déjà-vu, a feeling which is widely shared

The feeling of déjà-vu creeps over you when you feel like you have met a stranger before, or also when you have the sensation of having already experienced a totally fresh situation. According to an American study1, this strange impression is very widespread, since almost six out of ten people experience an episode of déjà-vu at least once in their lifetimes.

According to the same study, the feeling of déjà-vu decreases with age and could be encouraged by stress or tiredness. Apart from this, it might seem that this phenomenon could be more frequent in people with a higher level of sociocultural awareness, and in those who have travelled a lot.

A difficult phenomenon to explain

For two centuries, the sensation of déjà-vu has been a subject of fascination. It has inspired no less than thirty different explanations2. The explanations suggested range from the farfetched, like paranormal phenomena, to the more serious, based on neuropsychology. “It is a phenomenon which is very difficult to explain”, confirms Francis Eustache, Director of a research unit into cognitive neuropsychology and the functional neuroanatomy of the human memory (Inserm, University of Caen).

According to the specialist in the neuropsychology of the memory, it is possible to come up with a few hypotheses, nonetheless. When the illusion of déjà-vu occurs, “The road which leads to a memory is erroneous”. This means it could be the memory which is taking us on a wild goose chase. The situation experienced is a stimulus which may activate something in our memory; some kind of knowledge in connection with the event. This could induce a feeling of exaggerated familiarity, as if you are remembering a memory which doesn’t actually exist.

“You can place this feeling of déjà-vu in the same category as false memories”, explains Francis Eustache. According to him, it is a little bit like “the price to pay for the complex functioning of our memory”. In fact, this system is constantly under construction, so as to select the information or memory which is relevant. “This phenomenon, although complex, is completely normal. On the other hand, it should not be confused with certain symptoms of neurological diseases”, explains the researcher.

Epilepsy and the feeling of déjà-vu

The sensation of déjà-vu can, in fact, be the symptom of certain forms of epilepsy. This neurological condition involves a series of electrical discharges in the brain. There are many different types of epilepsy and an equally high number of symptoms associated with them, in terms of the cerebral regions affected.

“The feeling of déjà-vu that can be observed in certain epileptic patients occurs in the same way as in “healthy” individuals. On the other hand, the frequency is much higher, and episodes can take place several times a week for certain types of epilepsy,” explains Patrick Chauvel, Professor of Neurophysiology and a neurologist at the Hospital of Timone in Marseille (AP-HM, Inserm).

Thanks to measures taken by the neurologist and his team3, it seems that the feeling of déjà-vu is born in internal regions of the temporal lobe. “One of the hypotheses suggested is that it could be an abnormal synchronisation of our perception of the present and our use of memories”, explains Prof. Chauvel. The synchronisation of these two different fluxes of information could lead to the brain interpreting the present as though it were the past. “But this sensation of déjà-vu could equally be caused by something else, like the abnormal stimulation of the system which detects familiarity, during an event which is completely new” the neurologist adds.

This strange feeling of déjà-vu stems from the complex mechanisms in our brains. While the processes in play are the subject of even more hypotheses today, you can nevertheless be sure that the real explanation resides in the functioning of our neurological systems. All those theories of paranormal activity and other mystical interpretations can therefore be thrown out of the window.
What is deja-vu?
What is deja-vu?

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