Have you ever experienced being able to anticipate every word, every movement, nearly everything that will happen during the next few seconds? This sensation is commonly called the deja vu. Everyone will have already heard someone say that he had a sensation of deja vu, but in fact, it seems that only between 60–80% of us have actually experienced it.
This strange sensation is characterised by a feeling of familiarity with a current event but without the capacity to find associated memories. This can happen, for example, when you arrive in a new place for the first time (and you know for certain that it’s the first time), but you’ve got the feeling that you have been there before.
Over time, and still today, this sensation has several explanations such as the hypothesis of premonitory dreams, paranormal capacities, or second life. These different theories can be explained by the fact that science is still unable to fully understand this phenomenon.
Over the past decade, neuroscientists have grappled with this question. Today, two major scientific theories try to explain this phenomenon.
The first one, the Gestalt theory is proposed (mainly) by Anne Cleary of Colorado State University. Cleary and her colleagues assert that the deja vu (DV) phenomenon occurs when the arrangement of elements in a situation are similar to elements previously seen. For example, when you are entering a new library, the furniture arrangement can remind you of the arrangement of another library. The fact that you aren’t able to remember the other library can trigger a sensation of DV by inducing a sensation of familiarity without the capacity to find associated memories.
The second theory, the decoupled familiarity hypothesis is proposed by Moulin and O’Connor of Pierre and Marie Curie University and the University of St Andrews, respectively. They have an opposing view to Cleary, they suggest that the DV is not due to a visual similarity but more by a ‘glitch’ in the temporal lobe. This glitch would cause a false sensation of familiarity, which would be mistakenly interpreted by a metacognitive process. This clash between a sensation of familiarity and the awareness that this sensation is false would trigger a DV sensation. In order to demonstrate that the sensation of DV can be present even without vision, O’Connor and Moulin interviewed a blind male adult who experienced ‘normal’ DV sensation. This finding leads them to conclude that the DV phenomenon can be triggered by other modalities apart from visual modality (like in the gestalt theory of Cleary). Moreover, to strengthen their hypothesis, they advanced the fact that people suffering from temporal lobe epilepsy are more likely to experience this phenomenon. This would tend to show that the temporal lobe has an important role in DV sensation.
Of course, both of them try to assess their theories by controlled experiment. But here lies the major problem of studies on DV: We are currently unable to recreate a DV phenomenon in the laboratory. One experiment shows that the assessment methods (e.g., asking ‘Have you got a DV sensation?’) can cause up to 58% of sensation of DV even when the experience does not seek to cause a DV sensation. So, it seems clear that our current ways to test the DV phenomenon are not good ones.
But after all, one question can be asked: what’s the point of investigating the deja vu phenomenon? Is this just to contribute to the stock of human knowledge? Yes and no. The study of the DV phenomenon can allow us to better understand how the brain and memory work.
This phenomenon gives us a glimpse into the vastness of the complexity of the human brain. But, it can also be useful for patients with some pathology (e.g., epilepsy or those who are suffering ‘pathological deja vu’).
Imagine yourself as if your life were stuck in a loop. Every day the same people, talking about exactly the same thing, the same information in the newspaper, the same weather, the same cat crossing the street. This situation may look like fiction, as portrayed in the film Groundhog Day, but it does indeed exist. This is what happened to a 29-year-old British man, who claims to suffer from this pathology for six years now.
This article is just an introduction to the ever-widening field of research on deja vu. If you would like to explore more on this I would suggest you read the book The Deja Vu Experience by Alan Brown. There are also interesting articles on the blog of Chris Moulin.
Jonathan Fortier is a PhD student in neuropsychology at the University of Angers.
