Deja vu is the experience of feeling sure that one has witnessed or experienced a new situation previously The experience is frequently attributed to a dream, although in some cases there is a sense that the experience happened in the past.
The experience of deja vu seems to be quite common among both adults and children. In formal studies 70% of people report having experienced it at least once. References to the experience of deja vu are also found in literature of the past, indicating it is not a new phenomenon. It has been extremely difficult to evoke the deja vu experience in laboratory settings, therefore making it a subject of few studies. Recently, researchers have found ways to recreate this sensation using hypnosis.
In recent years, deja vu has been subjected to serious psychological and neurophysiological research. Scientifically speaking, the most likely explanation of deja vu is not that it is an act of precognition or prophecy, but rather that it is an anomaly of memory. It is the impression that an experience is being recalled. This explanation is substantiated by the fact that the sense of recollection is strong in most cases, but that the circumstances of the experience, such as when, where and how the experience occurred, are quite uncertain.
Likewise, as time passes, subjects can exhibit a strong recollection of having the unsettling experience of deja vu itself, but little or no recollection of the specifics of the event or circumstances they are remembering when they had the deja vu experience. In particular, this may result from an overlap between the neurological systems responsible for short term memory, events which are perceived as being in the present, and those responsible for long term memory such as events which are perceived as being in the past.
In other words, the events would be stored into memory before the conscious part of the brain even received the information and processed it. This would explain why one is powerless when trying to twist the outcome of the event in order to create a paradox. The delay is only of a few milliseconds and already happened at the time the consciousness of the individual is experiencing it.
Another theory being explored is that of vision. As the theory suggests, one eye may record what is seen fractionally faster than the other, creating that sensation of strong recollection upon the same scene being viewed milliseconds later by the opposite eye. However, this theory fails to explain the phenomenon when other sensory inputs are involved, such as the auditive part, and especially the digital part.
For instance, if one experiences deja vu of someone slapping the fingers on his or her left hand, then the deja vu feeling is certainly not due to his or her right hand to be late on the left one. Also, persons with only one eye still report experiencing deja vu. The global phenomenon must therefore be narrowed down to the brain itself, where one hemisphere would be late compared to the other.
Early researchers tried to establish a link between deja vu and serious psychopathology such as schizophrenia, anxiety, and dissociative identity disorder, with hopes of finding the experience of some diagnostic value. However, there does not seem to be any special association between deja vu and schizophrenia or other psychiatric conditions. The strongest pathological association of deja vu is with temporal lobe epilepsy. This correlation has led some researchers to speculate that the experience of deja vu is possibly a neurological anomaly related to improper electrical discharge in the brain.
Some believe deja vu is the memory of dreams. Though the majority of dreams are never remembered, a dreaming person can display activity in the areas of the brain that process long term memory. It has been speculated that dreams read directly into long term memory, bypassing short term memory entirely. In this case, deja vu might be a memory of a forgotten dream with elements in common with the current waking experience. This may be similar to another phenomenon known as deja reve, or already dreamed. However, later studies on mice indicate that long term memories must be first established as short term memories.
Not only is the link to dreams as they pertain to deja vu the subject of scientific and psychological studies, it is also a subject of spiritual texts, as is found in the writings of the Bahai Faith with quotes like “Behold how the thing which thou hast seen in thy dream is, after a considerable lapse of time, fully realized.”
John Lennon suggests that a feeling of remembering occurs in a sense that he might realize that what he had dreamt is now a relevant present action that is taking place right here right now:
I was once sitting down in the kitchen noticing that my plate seemed well too familiar, it seemed as if my head motions were foreseen, and that every move would trigger a continuation to happen. I had many deja vu’s as a child but this was extraordinary, I knew from the bottom of my heart that I had dreamed this situation years ago, as a little boy, that amazingly an entire piece of memory was regained and I finally understood when and where I was dreaming and how long this dream was, and most importantly how many years ago did I dream.
Those believing in reincarnation theorize that deja vu is caused by fragments of past life memories being jarred to the surface of the mind by familiar surroundings or people. Others theorize that the phenomenon is caused by astral projection, or out of body experiences, where it is possible that individuals have visited places while in their astral bodies during sleep. The sensation may also be interpreted as connected to the fulfillment of a condition as seen or felt in a premonition.
The term deja vu was coined by a French psychic researcher Emile Boirac in his book The Future of Psychic Sciences, which expanded upon an essay he wrote while an undergraduate. The experience of deja vu is usually accompanied by a compelling sense of familiarity, and also a sense of strangeness or weirdness.