The mysteries of the human brain are complex and impossibly numerous, especially considering that psychological science is essentially still in it’s infancy.With this in mind, it is easier to understand how a phenomenon such as deja vu has yet to be scientifically explained, despite how well-known and common it is. It is perhaps the uncanniness and mystery of this particular psychological occurrence that has bolstered its presence in the human imagination. Some of the more colorful attempts to explain deja vu include psychic experiences, messages from a higher power, or glimpses of a past life. As outlandish as some of these theories may be, they are still included in the over 40 competing theories on the causes of deja vu that currently exist in the world. This multitude of theories about deja vu can be explained by the difficulties encountered in trying to study the phenomenon. For one thing, deja vu is a completely personal experience, one which cannot be confirmed or refuted by an outside party. As such, it has not traditionally been given much scientific attention, banished instead to the realm of spiritualism and the occult. Also tricky is the timing of deja vu experiences: there is no reliable way to induce a deja vu experience, which is most often very fleeting, or to predict when an individual might experience one. Additionally, deja vu is not universal. According to a 2004 New York Times article, two thirds of surveyed adults reported having the experience, with frequent travelers, younger adults, and the highly educated experiencing it more often. Here are some of the more popular current theories from the scientific end of the spectrum:
The theory sometimes known as “familiarity without recall” posits that the deja vu experience is triggered when an individual comes across a set of stimuli that resemble, or have some elements of, a past experience. Ordinarily, this would trigger a feeling of familiarity. However, when the given stimuli has been experienced but is not consciously recalled by the individual that the uncanny feeling will arise. Researchers have pointed to evidence that people who travel, dream, and watch movies frequently are more likely to experience deja vu as support for this theory. These activities, which are likely to give an individual a wider range of experiences than those who do not engage in them, increase the chances the chances of encountering a familiar scene without specifically recalling the experience that is making it similar. One scientific experiment attempted to test this theory by giving participants lists of words to memorize, and then presenting them with a test list of cued words. For each word, participants were asked to recall a similar word on the first list, and were also asked, regardless of correct recall, whether the word was familiar or not. It was shown that even when a participant could not recall the actual word, they rated words that were similar to words on the memorized list as more familiar than complete novel words (i.e. HEMLOCK, HAMMOCK). A more recent study attempted to recreate the actual circumstances in which people experience deja vu to test this theory as well. Evidence has shown that places and scenes are the most likely stimuli to invoke deja vu. The researchers created over 100 different scenes which were divided into pairs that shared common layouts, such as chairs or objects in similar places. It was found that scenes that had similar layouts, but were distinctly different from one another in other ways, were the most likely to produce a feeling of deja vu for the study participants.
There is also a strong link between epileptic seizures and deja vu, specifically in patients with medial temporal lobe epilepsy. This region of the brain includes a structure known as the hippocampus, which plays a large role in memory function. A seizure is the result of abnormal electrical impulses in the brain, which leads to random signals being transmitted between neurons. These neuronal misfirings can lead to changes in perception, movement, and behavior in an individual, lasting anywhere from a few seconds to a few minutes. People with temporal lobe epilepsy in particular often report a feeling of deja vu as a common experience during a seizure. This has led some researchers to believe that deja vu in healthy individuals happens in a similar way: random electrical impulses between neurons can cause a brief and unsettling feeling of familiarity in a novel setting.
Another interesting theory implicates a malfunction of short and long-term memory storage mechanisms for deja vu experiences. This would mean that current sensory input, which is normally stored in our short-term memories before being processed by the brain into long-term memory, may every so often bypass the short-term and end up prematurely in long-term memory processing. This mix-up in memory storage may cause an individual to experience a current situation as if it had happened in a distant memory: deja vu.
Yet another theory points to neurotransmitters such as dopamine as the probable culprit for the deja vu experience. This is partially based on evidence that deja vu is experienced more often in people ages 15-25. Teenagers and young adults tend to have higher levels of dopamine naturally. A case study of a 39-year old man adds possible evidence to this theory. After coming down with the flu, the man was put on amantadine and phenylpropanolamine, medications known to increase dopamine activity in the brain, and after a short time, he was experiencing intense bouts of deja vu. The case study reports that after discontinuing the medication, the deja vu experiences disappeared.
Today, it remains to be seen whether the puzzling origins of deja vu will ever be definitively uncovered. Whether an existing theory holds the answer, or if a future discovery may reveal its cause, for now, it is a benign and delightfully mysterious occurrence that will surely continue to intrigue creatives and kooks the world over. And, of course, I would be remiss if I didn’t mention a glitch in the Matrix before the end of this article.
http://science.howstuffworks.com/science-vs-myth/extrasensory-perceptions/deja-vu2.htm
http://www.sciencedaily.com/releases/2008/11/081118122146.htm
http://www.nytimes.com/2004/09/14/science/14deja.html?pagewanted=1
http://www.scientificamerican.com/article.cfm?id=deja-vu-found-originate-similar-scenes
