Deja vu

The term déjà vu (French: "already seen", also called paramnesia) describes the experience of feeling that one has witnessed or experienced a new situation previously. The term was created by a French psychic researcher, Émile Boirac (1851–1917) in his book L'Avenir des sciences psychiques (The Future of Psychic Sciences), which expanded upon an essay he wrote while an undergraduate French concentrator at the University of Chicago. The experience of déjà vu is usually accompanied by a compelling sense of familiarity, and also a sense of "eerieness," "strangeness," or "weirdness." The "previous" experience is most frequently attributed to a dream, although in some cases there is a firm sense that the experience "genuinely happened" in the past.

The experience of déjà vu seems to be very common; in formal studies 70% or more of the population report having experienced it at least once. References to the experience of déjà vu are also found in literature of the past, indicating it is not a new phenomenon. However, in laboratory settings, it is extremely difficult to invoke the déjà vu experience, making it a subject with few empirical studies. Recently, however, researchers have found ways to recreate this sensation using hypnosis.

Types of déjà vu
According to Arthur Funkhouser there are three types of déjà vu:

Déjà vécu
Usually translated 'already seen' or 'already lived through,' déjà vécu is described in a quotation from David Copperfield by Charles Dickens: "We have all some experience of a feeling, that comes over us occasionally, of what we are saying and doing         having been said and done before, in a remote time - of our having been surrounded, dim ages ago, by the same faces, objects, and circumstances - of our knowing perfectly what will be said next, as if we suddenly remember it!"

When most people speak of déjà vu, they are actually experiencing déjà vécu. Surveys have revealed that about one third of the population have had these experiences, more often (and perhaps more intense) in people between the ages of 15 and 25. The experience is usually related to a very banal event, but is so striking that it is remembered for years afterwards.

Déjà vécu refers to an experience involving more than just sight, which is why labeling such "déjà vu" is usually inaccurate. The sense involves a great amount of detail, sensing that everything is just as it was before. Because of this, theories that the situation was just read about earlier or experienced in a previous life are invalid, as those experiences could not recreate the exact situation due to a lack of sense involvement or the presence of modern surroundings.

More recently, the term déjà vécu has been used to describe very intense and persistent feelings of a déjà vu type, which occur as part of a memory disorder. As described in Moulin, C.J.A., Conway, M.A. Thompson, R.G., James, N. & Jones, R.W. (2005). Disordered Memory Awareness: Recollective Confabulation in Two Cases of Persistent Déjà vecu. Neuropsychologia, 43 :1362-1378.

Déjà senti
Dr. John Hughlings Jackson recorded the words of one of his patients who suffered from temporal lobe or psychomotor epilepsy in an 1889 paper:

"What is occupying the attention is what has occupied it before, and indeed has been familiar, but has been for a time forgotten, and now is recovered with a slight sense of satisfaction as if it had been sought for. ... At the same time, or ... more accurately in immediate sequence, I am dimly aware that the recollection is fictitious and my state abnormal. The recollection is always started by another person's voice, or by my own verbalized thought, or by what I am reading and mentally verbalize; and I think that during the abnormal state I generally verbalize some such phrase of simple recognition as 'Oh yes - I see', 'Of course - I remember', &c., but a minute or two later I can recollect neither the words nor the verbalized thought which gave rise to the recollection. I only find strongly that they resemble what I have felt before under similar abnormal conditions."

This phenomenon specifies something 'already felt.' Unlike the implied precognition of déjà vécu, déjà senti is primarily or even exclusively a mental happening, has no precognitive aspects, and rarely if ever remains in the afflicted person's memory afterwards.

As with Dr. Jackson's patient, some temporal-lobe epileptics may experience this phenomenon.

Déjà visité
This experience is less common and involves an uncanny knowledge of a new place. Here one may know his or her way around in a new town or landscape while at the same time knowing that this should not be possible.

Dreams, reincarnation and also out-of-body travel have been invoked to explain this phenomenon. Additionally, some suggest that reading a detailed account of a place can result in this feeling when the locale is later visited. Two famous examples of such a situation were described by Nathaniel Hawthorne in his book Our Old Home and Sir Walter Scott in Guy Mannering. Hawthorne recognized the ruins of a castle in England and later was able to trace the sensation to a piece written about the castle by Alexander Pope two hundred years earlier.

C. G. Jung published an account of déjà visité in his 1952 paper On synchronicity.

In order to distinguish déjà visité from déjà vécu, it is important to identify the source of the feeling. Déjà vécu is in reference to the temporal occurrences and processes, while déjà visité has more to do with geography and spatial dimensions.

Scientific research
In recent years, déjà vu has been subjected to serious psychological and neurophysiological research. The most likely candidate for explanation, according to scientists in these fields, is that déjà vu is not an act of "precognition" or "prophecy" but is actually an anomaly of memory; it is the impression that an experience is "being recalled" which is false. This is substantiated to an extent by the fact that in most cases the sense of "recollection" at the time is strong, but any circumstances of the "previous" experience (when, where and how the earlier experience occurred) are quite uncertain. Likewise, as time passes, subjects can exhibit a strong recollection of having the "unsettling" experience of déjà vu itself, but little to no recollection of the specifics of the event(s) or circumstances they were "remembering" when they had the déjà vu experience, and 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 (events which are perceived as being in the past).

Links with disorders
A clinical correlation has been found between the experience of déjà vu and disorders such as schizophrenia and anxiety, and the likelihood of the experience increases considerably with subjects having these conditions. However, the strongest pathological association of déjà vu is with temporal lobe epilepsy. This correlation has led some researchers to speculate that the experience of déjà vu is possibly a neurological anomaly related to improper electrical discharge in the brain. As most people suffer a mild (i.e. non-pathological) epileptic episode regularly (e.g. the sudden "jolt", a hypnagogic jerk, that frequently occurs just prior to falling asleep), it is conjectured that a similar (mild) neurological aberration occurs in the experience of déjà vu, resulting in an erroneous sensation of memory.

Pharmacology
It has been reported that certain recreational drugs increase the chances of déjà vu occurring in the user. Interestingly, some pharmacological drugs, when taken together, have also been implicated in the cause of déjà vu. Taiminen and Jääskeläinen (2001) reported the case of an otherwise healthy male who started experiencing intense and recurrent sensations of déjà vu on taking the drugs amantadine and phenylpropanolamine together to relieve flu symptoms. He found the experience so interesting that he completed the full course of his treatment and reported it to the psychologists to write-up as a case study. Due to the dopaminergic action of the drugs and previous findings from electrode stimulation of the brain (e.g. Bancaud, Brunet-Bourgin, Chauvel, & Halgren, 1994), Taiminen and Jääskeläinen speculate that déjà vu occurs as a result of hyperdopaminergic action in the mesial temporal areas of the brain.

Memory-based Explanations
The similarity between a déjà vu-eliciting stimulus and an existing, but different, memory trace may lead to the sensation. Thus, encountering something which evokes the implicit associations of an experience or sensation that cannot be remembered may lead to déjà vu. In an effort to experimentally reproduce the sensation, Banister and Zangwill (1941) used hypnosis to give participants posthypnotic amnesia suggestions for material they had already seen. When this was later re-encountered, the restricted activation caused by the posthypnotic amnesia resulted in three of the 10 participants reporting what the authors termed paramnesias. Memory-based explanations may lead to the development of a number of non-invasive experimental methods by which a long sought-after analogue of déjà vu can be reliably produced that would allow it to be tested under well-controlled experimental conditions.

Neuronal Theories
In the late 19th and early 20th Centuries, it was widely believed that déjà vu could be caused by the mis-timing of neuronal firing. This timing error was thought to lead the brain to believe that it was encountering a stimulus for the second time, when in fact, it was simply re-experiencing the same event from a slightly delayed source. A number of variations of these theories exist, with miscommunication of the two cerebral hemispheres and abnormally fast neuronal firing also given as explanations for the sensation. Perhaps the most widely acknowledged neuronal theory is the optical pathway delay theory which explains déjà vu as being the product of a delayed optical input from one eye. Closely following the input from the first eye (when it should be simultaneous), this misleads conscious awareness and suggests a sensation of familiarity when there should not be one. Although intuitively plausible, this theory is untestable due to the minute times involved in neuronal firing, and inconsistent with reports that blind individuals experience déjà vu in the same way as sighted individuals (O'Connor & Moulin, 2006).

Parapsychology
Déjà vu is associated with precognition, clairvoyance or extra-sensory perceptions, and it is frequently cited as evidence for "psychic" abilities in the general population. Non-scientific explanations attribute the experience to prophecy, visions (such as received in dreams) or past-life memories.

Dreams
Déjà 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. Perhaps a dream can read directly into long-term memory, bypassing short-term memory entirely. In this case, déjà vu might be a memory of a forgotten dream with elements in common with the current "awake" experience. This may be similar to another phenomenon known as deja rêvé, or "already dreamed."

Related phenomena

 * Jamais vu: From the French, meaning "never seen," the expression means explicitly not remembering having seen something before. The person knows it has happened before, but the experience feels unfamiliar. Often described as the opposite of déjà vu, jamais vu involves a sense of eeriness and the observer's impression of seeing the situation for the first time, despite rationally knowing that he or she has been in the situation before. Jamais vu is sometimes associated with certain types of amnesia and epilepsy. An old internet joke referred to this feeling as "vujà dé."
 * Presque vu: From the French language, meaning "almost seen," the expression means almost, but not quite, remembering something. Often very disorienting and distracting, presque vu rarely leads to an actual breakthrough. Frequently, one experiencing presque vu will say that they have something "on the tip of their tongue". Presque vu is often cited by people who suffer from epilepsy or other seizure-related brain conditions, such as temporal lobe lability.
 * Déjà éprouvé: "already attempted or tried"

Popular references

 * In the 1999 film The Matrix, the character of Neo experiences déjà vu (though the experience somewhat differs: Neo sees a black cat go past twice consecutively). Trinity explains to Neo that "a déjà vu is usually a glitch in the Matrix. It happens when the Machines change something."
 * In the 1998 anime Card Captor Sakura, the character of Sakura experiences déjà vu, caused by a Clow Card.
 * The 1993 film Groundhog Day documents a rather pertinent (to the main character, at least) realisation of this phenomenon.
 * Déjà vu is a 1989 Polish-Soviet comedy film by Juliusz Machulski.
 * Déjà vu is the name of a Giant Inverted Boomerang ("Super Invertigo") roller coaster by Vekoma that is operating at Six Flags Great America, Six Flags Magic Mountain and Six Flags Over Georgia.
 * Dionne Warwick had a Top 20 hit single, "Deja Vu" in 1979.
 * Comedian George Carlin invented an alternate phenomenon he called vujà dé, or "the feeling that somehow, none of this has ever happened before!"
 * Deja vu is the name of a Silver Age Batman villain.
 * American singer/songwriter John Fogerty wrote a song called (somewhat redundantly) "Déjá Vu (All Over Again)."
 * Decades before, however, Yogi Berra said "It's like déjà vu all over again" (one of many famous Yogiisms.)
 * Crosby, Stills, Nash & Young recorded a song called "Deja Vu" for an album of the same name in 1970. The song's recurring theme was David Crosby singing "... and I feel like I've been here before."
 * There is a short story by Stephen King called "That Feeling, You Can Only Say What It Is in French", which deals with a subject's horrifying deja vu experiences.
 * Deja Vu is also the name of a band from the Faroe Islands which plays rock/pop music.
 * The Spice Girls sing "tell me will this déjà vu ever end..." in their song "Say You'll Be There".
 * Deja Vu is the name of a computer game and NES game published by Seika.
 * Deja Vu, Presque Vu and Jamais Vu are mentioned in Joseph Heller's 1961 novel Catch-22 and play a large role in Kim Stanley Robinson's 1996 novel Blue Mars.
 * Deja Vu is also the name of an Iron Maiden song.
 * "Jamais Vu" is the name of a song written by alternative band Dredg.
 * The term Deja vu was used in the Charmed season 1 episode Deja vu all over again as Tempus resets time to succeed in killing all three Charmed ones.
 * Deja Vu is also the name of the second campaign mission for the Soviets in the computer game Yuri's Revenge, as it put the player on the opposing side of an Allied mission from the original Red Alert 2.
 * The band Dream Theater has a song called "Strange déjà vu".
 * "Déjà Vu" is a 2006 song by Beyoncé Knowles featuring Jay-Z.
 * "Déjà Vu" is a song by the Yeah Yeah Yeahs.
 * "Déjà Vu" is a song by brazilian singer Pitty.
 * "Déjà Vu" is the 2006 Action/Adventure, Romance, Science Fiction/Fantasy and Thriller Movie By Walt Disney Pictures & Jerry Bruckheimer Films. Actor Denzel Washington. Release Date: November 22nd, 2006 (wide)
 * The band Ace of Base recorded a song entitled "My Déjà Vu" on their 1995 album "The Bridge"