Something you are seeing for the first time seems familiar. While sensing something new, you feel as if you had sensed it before. On visiting a place for the first time in life, you feel like you had been there before. In these I-have-seen-this-before or I-have-been-here-before kind of experiences, you cannot recollect the last time you experienced something very similar to what you currently are. You feel like you had experienced it in reality or perhaps in your dreams. If anything like this has happened to you, you have experienced Deja vu.
Emile Boirac, a French researcher in psychology, coined the term, Deja vu in an essay about this interesting phenomenon. Most of those who experience Deja vu, claim to have been through a similar experience in the past, in their dreams or in reality.
Types of Deja vu
Deja Senti: This feeling refers to something 'already felt'. It is a mental phenomenon and researchers believe that something felt in the past may be very similar to something felt in the present. Two different events can generate similar feelings and a person associates a present feeling with a similar one in the past, thus experiencing what is known as Deja senti. The similarity in the emotions associated with both events, makes a person think that he has felt the same before.
Deja Vecu: A feeling that everything that is happening currently is identical to what had happened before and a strange idea about what is going to happen next, is termed as Deja Vecu. A person experiencing a Deja vecu feeling claims to know what is going to happen in the near future and often feels that he is remembering it.
Deja Visite: This form of Deja vu is a feeling of having visited a place before even when visiting it for the first time. A person experiencing this form of Deja vu claims to have the knowledge of that place. He claims to be completely aware of the geography of that place. He thinks he has visited the place even when the contrary is true. In many cases of Deja Visite, the individual experiencing it is found to be knowing the place well although he has never visited it.
Since long, researchers have been trying to find the exact reasons behind Deja vu. Disorders like schizophrenia and certain neurological diseases are said to cause it. However, researchers have not achieved much success in establishing the exact relationship between the two. Even high levels of anxiety are said to cause Deja vu. Research says that it can result from the mal-functioning of the brain's electrical system. The feeling is attributed to incorrect sensation of memory.
Prolonged use of certain medicines can also cause Deja vu. Some examples include amantadine and phenylpropanolamine. Certain medicinal drugs can cause a hyperdopaminergic action in the mesial temporal areas of the brain, resulting in Deja vu.
The human brain is a highly complex organ. It tends to derive associations between different situations. Often, it tries to experimentally reproduce a situation that it has never faced before. Thus, one's own anticipation of a certain incident may make the person think that he has encountered it in the past.
Interestingly, it may so happen that one eye perceives a certain thing before the other. One eye records the incident earlier. The other eye, which records the same incident milliseconds later, makes the brain get a feeling of recollection. One eye perceives something and the brain interprets it. The other eye that lags in time by a few milliseconds perceives the same thing and sends the image to the brain. As the brain perceives the same thing some time later, the person believes to have seen it before. But perhaps this reason is incorrect. That's because even people with one eye experience Deja vu.
While researchers and psychologists try to find the reasons to Deja vu in science, others explore something beyond. Some theories attribute it to psychic abilities that some human beings possess, while others say that these feelings are a result of past-life experiences. Indeed, Deja vu is a mysterious feeling and its reasons too are mysterious.