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Tuesday, November 5, 2013

We have all had some feeling of déjà vu. The experience of being someplace or doing something that we had done before, but can’t remember exactly where or when. The feeling is strong and strange but the effects are brief. Researchers have struggled to explain, with little success, why we have these complex sensations. There are many theories about the causes of déjà vu, and none of them are mutually exclusive. Déjà vu might be generated by multiple factors.

Here for your consideration are the eight most common theories why déjà vu occurs, in the order of their historical recognition:

1. The déjà vu experience is a manifestation of a wish fulfillment, or a subconscious repetition of a past experience (late 19th Century psychology). This is an early Freudian-like theory about the experience; but it implies a conscious effort on the part of the individual. Déjà vu experiences are not believed to be under the control of the individual. They are experiences that a person is not able to either create or ignore.

2. Déjà vu is a symptom of reincarnation; a person living their lives for a second time (late 19th Century parapsychology). This is an unorthodox theory, of course, but has been given new attention. Embrace this theory at your own risk. Recent research in physics has found that particles (tachyons) possibly travel backwards in time and that photons can exist in two places at once. Neurological time travel can no longer be dismissed automatically. There is also a growing belief in “genetic memory” (memories encoded in one’s genes and passed on to new generations).

3. It is caused when a person gets a glimpse of a place or situation and a memory is created before a fully conscious perception is made (1928). The result is a false sense of familiarity. While this theory might account for the feeling that an experience is being “recalled,” most researchers agree that a conscious perception needs to occur before, and not after, a memory is generated.

4. Déjà vu is trigged by the presence of a serious psychological disorder, like schizophrenia or extreme anxiety (1930-1940). This was researched extensively in the Thirties, but a link between déjà vu and psychological disorders was generally not found. The vast number of people reporting déjà vu experiences did not have known disorders. There is, however, an association between the experience and temporal-lobe epilepsy. Most people have had very mild but sudden epilepsy-like electrical discharges in the brain; like the jolt you may feel just before falling asleep.

5. Déjà vu episodes are a result of an interaction of multiple drugs; creating a surrealistic or hallucinogenic experience (1970’s). Numerous cases have been reported where drug interactions and déjà vu coincide and many researchers believe there is a cause and effect relationship present. But since most people who experience déjà vu are not taking multiple pharmaceutical drugs at the same time, this explanation is not viewed as widely applicable.

6. There is a slight malfunctioning between the long-term and short-term memory circuits of the brain (1980's - 1990’s). An overlap of neurological system processes causes a memory to be created before the conscious part of the brain recognizes the experience. This is a variation of theory #3 (above) from the 1920’s, BUT the body’s electrical system does do something similar in reacting to stimulus. You probably remember from school learning about the “reflex arc” where your hand, if placed on a hot stove, will pull away from the stove even before you are aware of the heat. Maybe short term memory works like this also.

7. Déjà vu results from the occasional mismatches made by the brain in its continuous attempt to create a whole picture out of very small pieces of information (2005). Only bits of sensory information are needed for the brain to reconstruct entire, three-dimensional images. When the brain receives these bits of input that are very similar to an experience from the past, an entire memory is brought forward. The brain has mistaken the past to be present - a mismatching of past and present sensory information. To the person having déjà vu, this explanation may be very unsatisfactory.

8. It is caused by problems of episodic memory resulting from similarities between new and old experiences (2012). Some researchers theorize that the hippocampus (a neuron cluster in the mid-brain) can become confused by new verses old, but familiar, experiences - a “confusion of episodes.” A person’s ability to distinguish between slightly different places and experiences can fade with time, and age. Older individuals still form memories but struggle between similar, but distinct, events. Yet the highest incidence of déjà vu is among people 15 to 25 years old. So something else must also be going on.

It seems that no single theory about déjà vu can be applied to all cases, and that various causes may indeed contribute to our experiences. Is it worth our time to research déjà vu occurrences? It may only be a quirky brain trick that most of us expect from time to time.

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