Déjà Vu All Over Again
Most people at some time in their lives have experienced the rather curious sensation of déjà vu, the feeling that you are reliving a certain moment of your life. It is a phenomenon that has fascinated the world for centuries. Novelists have written about it, movies and television shows have described it and psychologists and neuroscientists have endeavored to explain it from a scientific perspective. This web paper will endeavor to explain how and why we experience the sensation of familiarity known as déjà vu as well as its connection to one of the most mysterious functions of the human brain: memory. By studying déjà vu we may gain insight into the complex relationship between the unconscious part of the nervous system that processes experiences and the neo-cortex that turns them into the stories we call memories.
In his novel David Copperfield, Charles Dickens very accurately describes the sensation of déjà vu as 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”  The term “déjà vu” literally meaning “already seen” is a little inaccurate. As a recent study published by the University of Leeds shows, it is possible for a blind man to experience the sensations of an already lived moment through his other senses: taste, smell, touch and hearing . What most people call déjà vu can be better described as “déjà vécu” “already experienced” a phenomenon that can involve all the senses of the nervous system.
To people suffering from the more serious, chronic déjà vu every new situation can feel like something they have already lived through. They can experience terrible depression and can be often misdiagnosed as delusional or epileptic. The other, milder form of the condition is more prevalent with about two-thirds of adults reportedly experiencing the sensation at one time in their lives , . Various factors seem to influence the frequency of the sensation. Déjà vu is more likely to occur during periods of strain and fatigue. It is more common in the younger population and is also experienced more frequently by well-traveled, well-educated and imaginative people .
Despite its prevalence in our society, for a long time déjà vu remained “filed away in a drawer marked ‘interesting and insoluble’”. Because there are no quantifiable outward symptoms, only a fleeting feeling of having seen something before, the phenomenon is not easily studied in a laboratory setting. In the past few decades however, scientists have made further investigations into the elusive sensation of déjà vu and its relation to the processes of memory and cognition , .
According to Dr. Alan Brown, a professor of psychology at the Southern Methodist University the causes of déjà vu can be classified into four categories. The first of these is the “dual processing” theory. The sensation of reliving a moment may be due to the activation of our familiarity system and malfunction of our retrieval system. While the two are generally in sync, a brief uncoordinated moment may result in something seeming familiar that cannot be exactly recalled .
Déjà vu can also be explained from a neurological perspective. The phenomenon may be caused by small, brief seizures possibly due to neural firing in the parahippocampal cortex, a region known to be associated with the ability to detect familiarity. These seizures are akin to those caused by epilepsy and indeed, many epileptics report experiences of déjà vu just before an attack . Moreover, it is possible to produce experiences of déjà vu in a laboratory by electrically stimulating parts of the temporal lobe .
The third theory explaining the déjà vu experience is based on the idea of unconscious memories. We often see, hear, smell or taste things that we do not really register. These sites, sounds, smells and tastes are unconsciously imprinted on our memories. When we see them once again therefore, they trigger a strong feeling of familiarity that cannot be attributed to a conscious memory . This theory is illustrated very well by a study conducted by Brown and Elizabeth Marsh a psychologist at Duke University. Students were shown a number of photographs of various buildings on a different campus and asked to locate a cross on each one. A week later they were shown the same photographs along with a set of new ones and asked to identify if they had ever been to any of the places in the pictures. The results of the study so far show that the students were much more likely to say they had actually been to a building if it were one of the ones they had initially been exposed to while searching for the cross. This suggests that the buildings were imprinted on the student’s unconscious when they first saw them and that this feeling of familiarity is completely independent of the I-function .
It is important to note that these unconscious memories do not necessarily have to result from outside information. This emphasizes one of the most fascinating things about the brain, the fact that many of its processes are completely internal. It is possible for example to experience déjà vu from something you have never actually done but perhaps only dreamed of or just imagined .
The final theory proposed by Brown to explain déjà vu is the theory of “double perception,” the idea that an interruption in our normal memory processes might make things appear falsely familiar . The theory can be explained by a study conducted by cognitive psychologists Larry L. Jacoby and Kevin Whitehouse in 1989. Subjects were shown a list of words on a screen and asked to memorize them. Some time afterwards, the subjects were shown a new set of words half of which had been on the original list and asked to identify the ones that they had seen before. The researchers discovered that if they flashed a word subliminally for a very short time before its official appearance on the screen the subjects were more likely to incorrectly identify it as a word from the original list. By seeing the word unconsciously and then giving it their full attention the subject’s subconscious was creating a sense of false familiarity. . This fact is not in the least surprising when one considers that our nervous system is constantly making things up and filling in the gaps in our perception. If it is possible for the brain to fill in a blind spot completely independent of the I-function then it is quite possible that for it to create memories that were never really there.
Each of these four theories goes a long way towards elucidating the sensation of déjà vu. It is doubtful that one of them should prove to be more correct than the others. The brain has so many different ways of doing even the simplest tasks that it is quite probable that each theory may account for a slightly different kind of experience.
To me, the most interesting aspect revealed by this compilation of research about the déjà vu phenomenon is the light that it sheds on the important role the I-function plays as a storyteller and its relationship to the rest of the nervous system. The unconscious nervous system is taking in, and processing all sorts of information both external and internal. It functions through a series of independent modules interacting with the outside world and with each other and it manages all this with out any sense of self being involved. The storyteller part of the brain, the neo-cortex has only a restricted capability to handle all the different variables and signals from the unconscious nervous system. Déjà vu then is an illustration of the way that the neo-cortex processes the various pieces of information it receives into a story.
In their study with the words flashing on a screen Jacoby and Whitehouse further discovered that when the subliminal flashing period was slowed down, allowing enough time for the subjects to read the words, the rate of inaccuracy was significantly less. It would seem that with shorter time periods for the subliminal messages, the unconscious mind, always filling in the blank, leapt to the conclusion that the words had already been seen. When the subjects had extra time to read the words, their I-function was able to take over and come to the conclusion that the word was not one of the ones on the original list .
These findings suggest that the experience of déjà vu supports the idea of a frequent conflict between the unconscious nervous system and the conscious I-function of the neo-cortex. The subliminal messages can be perceived as primary emotions, felt by the unconscious part of the nervous system before the information can be imparted to the I-function. With the longer time periods, the I-function has time to create a story that may counter the primary emotion of familiarity registered by the unconscious. While the emotion of familiarity is an unconscious experience, the idea of time and cause and effect exist only in the neo-cortex. As Dr. Moulin a psychologist at the University of Leeds puts it: “déjà vu is a feeling or conflict of two opposing sensations—one, which is the feeling of familiarity, the other the objective knowledge that you haven’t encountered the situation before”.
Although déjà vu can be chronic and detrimental to a person’s mental health, mild déjà vu attests to something that is necessary for our survival and our humanity. The conflicts between the unconscious nervous system and the I-function allow us to constantly revisit and refine our own memories and stories. The I-function is constantly reworking, rethinking and re-imagining how we define the world around us and ourselves. It is this capacity for change that makes us truly human.
http://www.canada.com/ottawacitizen/news/story.html?id=2c4f7afd-5a3a-4e52-a2fb-bc729692bfb4 When déjà vu is more than just a feeling, Sharon Kirkey
 http://www.msnbc.msn.com/id/15937167/, Blind man has déjà vu, busting a myth: Case study contradicts theory of optical pathway delay
http://www.nytimes.com/2004/09/14/science/14deja.html?pagewanted=1&ei=5088&en=33156dc1dff26362&ex=1252900800&partner=rssnyt, Déjà Vu: If It All Seems Familiar, There May Be a Reason, Benedict Carey
 http://chronicle.com/free/v50/i46/46a01201.htm, The Tease of Memory, David Glenn
 http://news.bbc.co.uk/2/hi/health/5194382.stm, Déjà vu recreated in laboratory