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DEJA VU, what you didn’t know about it!

Updated: Jun 20, 2023

Occasionally, almost everyone has experienced the feeling that a present situation has been re-lived before.

What is Deja Vu?

The term deja vu derives from the French phrase that translates as “already seen”. This expression was firstly used by Emile Boirac in his L’Avenir des Sciences Physiques, a study that dated back to his bachelor dissertation at the University of Chicago. Deja vu, is therefore defined as an intense feeling in which a person experiences an event that has re-occurred in the past. This is followed by an inaccurate feeling as well as a strange sense of familiarity.

Three kinds of Deja Vu

Most people are familiar with deja vu which forms just one category of the phenomenon.

According to Arthur Funkhouser, there are three different kinds of deja vu: deja vecudeja senti and deja visiteDeja vecu, is the correct term of the renown deja vu and translates to “already lived”. This feeling has a more intense impact, considering that it is much more vivid than just a visual stimulus. The feeling of the incident is much more detailed in information and the person who experiences it feels that everything is just like a incident which has “occurred” in the past. Deja senti, is related to a certain feeling and translates to “I have felt it”. In contrast with the previous two terms, deja senti does not contain any suspicion of prognosis, which makes it a completely normal event. Finally, deja visite, is connected to a paradoxical feeling that one is familiar with a place they have never visited before. There are people who visited a city for the first time and they knew by heart how to reach their final destination… This is a very rare experience and there are many theories to explain this phenomenon: from extracorporeal experiences and interstellar travel to logical answers. The distinguishing feature between deja vecu and deja visite is that deja vu is filled with emotions while deja visite is mainly related to geographical and spatial perceptions. 

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One in two experience Deja Vu!

It has been noticed that deja vu started to occur many centuries ago and there is a high chance that it started from the first moment of humans on planet Earth. According to many studies there is a high number of people who experience deja vu! In 1890, Lack-Szyrma, on behalf of the scientific community researched similar incidents. In 1954, McKellar wrote one of the first studies on the phenomenon and concluded that 23% of the world population are experiencing deja vu. Twelve years later, this percentage, skyrocketed to 80%, when C.E.Green questioned 115 students from the University of Southampton. The vast majority of the respondents agreed that they had experience deja vu at least once during their lifetime! Later on, in 1985 a relevant research by Haraldsson showed that 64% of the British and Irish population has experienced deja vu, while he calculated the respected percentage for the USA, which was down to 60%! Finally, in 1999, Shari A. Cohn made a study where she contacted 208 people from across Scotland, Britain, Europe, North America, and other parts of the globe. The study revealed that the percentage of people who have experienced deja vu was up to 66%. 12% were not sure if they had experienced the phenomenon, while 22% replied negatively!

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Why are the clinical studies not possible?

Having stated all of the above it is normal to wonder why deja vu was never a subject of scientific research and experiment. The answer is simple and it is related to the experiences. Deja vu can only be experienced at random moments. Therefore, it is very uncertain to predict when it will occur next and this is the reason why the study of deja vu can only be processed through statistical researches and not clinical studies.

Pharmaceutical side-effect or neurological disorder?

There are dozens of theories that try to explain the paradoxical phenomenon. One of them revealed the remarkable similarities between deja vu and some mental disorders like schizophrenia. Most similarities have been observed between deja vu and transient epileptic amnesia (TEA), which leads scientists to believe that deja vu may be a neurological abnormality. What does that mean though? Most people suffer from minor non-pathological seizures, which may probably lead to the deja vu experiences! Another interesting theory approaches the same topic on a different level. Clinically, it has been proved that the combined use of specific drugs increases the chance of experiencing deja vu. In 2001, Taiminen and Jaaskelainen reported the case of a healthy man who started to experience repetitive and intense incidents of deja vu when he followed a pharmaceutical prescription, which combined amantadine and phenylpropanolamine to prevent a simple flu. A 19th century study, is also interesting as it links deja vu to neural delayed activation. This process is sufficient enough to trick the human brain to accept a similar stimulus with a slight delay. The most relevant theory was that of a visual delay which explained that the deja vu effect is the result of delayed information which is being transferred from one eye to the brain while the other eye processes the information normally. Thus, the same stimulus reached the brain with a millisecond’s delay, which was enough to mislead the consciousness and create a paradoxical sense of intimacy that bests describes the deja vu phenomenon. As scientific as this theory may appear, it was soon turned out to be wrong when deja vu cases occurred to blind people. 

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Deja Vu: An unknown human ability 

Except for the scientifically approached theories, there are some others from the area of parapsychology… Μany scientists have linked the experience to prognosis phenomena, clairvoyance, and supersensitive perceptions. A big part of the psychic research community has linked deja vu to mental capacities that the majority of people may have. On the other hand, some researchers support the idea that deja vu is linked to dreams that contain memory fragments! According to this theory, dreams – like any other important stimulus – are stored in the long-term memory of the brain. Even though most people could not recall the vast majority of their dreams, a human can store their dreams in a specific part of their brain. Thus, there is a high chance that the dream might ignore the short-term memory part of the brain and move directly to the long-term one. In a few words, deja vu might occur due to the anamnesis of a forgotten dream which has a lot of common elements to an event a person is experiencing during a specific moment. 

Deja Vu was recreated in a research lab!

All of the above are just theories that were developed in an attempt to find answers for the phenomenon since it cannot be clinically studied. In July 2006, BBC broadcasted a piece of news, which stated that “Deja vu experiences were recreated in a lab!” What does this mean though? Since they managed to recreate such an experience in the lab that mean that the phenomenon can be clinically studied! According to New Scientist, Leeds Memory Group members managed to experience deja vu events through the method of hypnosis. The article argued that “this reproach will light the fundamental processes of the human memory”.

How did they end up to this discovery? According to the majority of scientists, when a human recognizes a familiar object or a face they go through two very important stages. Firstly, the brain is accessing a part of our memory to determine if an object which is being seen at that specific time, has been observed in the past by the human eye. If the object is recognized, then it is immediately marked as a familiar one. Within the research lab, through the method of hypnosis, scientists were able to separate the second process from the first one which resulted in the participants to experience deja vu. The result of the Leeds Memory Group study was presented to the National conference of Memory, in Sydney, by Akira O’ Connor. The entire scientific community was moved by their results.


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