Deja vu is a french term that means "already seen" and some of it's variations are deja rencontre, already met; deja eprouve, already experienced; deja senti, already thought; deja visite, already visited. There are a lot of theories as to why this complex phenomenon happens. Some say its reincarnation, others thought of it as a memory glitch and some others believe it is caused by stress. Among all of these claims, researchers are able to put déjà vu into two general categories: associative déjà vu and biological déjà vu.
The most common one is the associative type where nature and senses play a vital role. It's like you see, smell, hear, or simply experience something that stirs a feeling and then you tend to associate it with what you've seen, smell, hear or experience before. Several researchers say that this is a memory-based type of déjà vu and assumed to be controlled by the memory centers of the brain. Biological déjà vu on the other hand, is closely linked to temporal-lobe epilepsy. People suffering from this illness, experience déjà vu just before the seizure take place. This is considered different from the typical déjà vu since the person experiencing it truly believe that he's been through that exact state before, rather than getting a feeling of familiarity that quickly passes.
The cause of deja vu may still be unclear. But one thing is for sure, it is among the paranormal events that only happen to certain people. It is a lot more rare than everyone seem to think it is and should not be confused with other paranormal phenomenon, especially with precognition (It is when a person feels that he know exactly what's going to happen next, and it does take place). An important difference is that, unlike precognition, a person who experiences deja vu does not have any idea that something is going to happen, but merely has the sensation of having already experienced the scene. Despite the difference, one theory is trying to prove the connection between precognitive dreams that gives a "deja vu feeling" afterwards. This however, is under further analysis.
Researchers admit that studying deja vu is extremely puzzling to the fact that it only occurs in a fraction of a second with no physical manifestations or witnesses, other than the person experiencing it. They are skeptical at inducing certainty on any reported incidents of déjà vu since there are no visual, audible, or maybe sensible evidence to prove it. Their studies are solely dependent on personal memories and descriptions in order to gather data. So many theories but still no definite explanations. Maybe déjà vu is just simply a part of human fantasy or perhaps a brain's slight misregister of mixing up the present from the past ... who knows? Apparently, there is a serious need for more systematic examinations to be done.
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