Déjà vu: On the tip of the mind

All of us have, at some point of our lives, faced a certain situation where you have that eerie sensation that you have already experienced the same situation before, but can't really place it. For example, after you go to a restaurant for the first time, it feels so familiar. But you know you never went to that particular place before.

This sensation of experiencing the unexperienced is called déjà vu, which literally translates from French to 'already seen.' It is a common feeling, as around 70 percent of the population of the world have experienced déjà vu. It is most common among the age group 15-20, and decreases with age. Déjà vu is most likely to happen if we are tired, distracted or in an unfamiliar setting. Déjà vu feels like if something is just on the tip of our mind, just like a word on the tip of our tongue.

The popular 1999 film "The Matrix" depicts déjà vu as 'a glitch in the matrix', the matrix being a simulation that all of mankind is living in. But considering that we probably don't live in a simulated reality, this is highly unlikely. Still, we are not exactly sure about what causes déjà vu. The fact that this happens almost randomly makes it that much harder to replicate it in controlled situations for scientists to examine it.

However, researchers have found some success in triggering déjà vu in volunteers by making them play a game or see a typed word, then suggest to forget or remember it, and show it to them again. Hypnosis and virtual reality also succeeded in certain cases. From these results, we can get ideas to explain déjà vu. The most widely accepted theories behind déjà vu are:

Split Perception Theory:  Déjà vu may happen if a person experiences a sensory twice successively, where the first is brief or distracted. The second time, the sensory is done consciously. This may happen if we were distracted by something and saw something else sub-consciously. Then, when we concentrate on it again, it may feel like we saw it before, as in a sense, we did. 

Dual Processing: Imagine someone dropping a glass from his hand. Your brain starts to process the information, which zips through pathways to reach the brain. This theory suggests that if any one of the details is a bit out of sync, then our brain thinks that they are two different occurrences. This can also happen if you have a dominant eye, which most of us do. The data from the dominant eye reaches the brain earlier than the other eye's. The delay is just a few milliseconds, but that is enough to incite the feeling of déjà vu. 

Implicit Memory:  Recognition memory enables to realize if you experienced an event or activity before. When we experience déjà vu, our recognition memory may be triggered, though we never encountered the situation. This may happen due to the presence of a familiar object or pattern. In an experiment, the test subjects were shown an image of a forest with trees and bushes, and later an image of garbage, piled in the same spatial layout of the bushes in the first image. This triggered déjà vu in participants.

Reconstruction of a memory:  Another possible cause of déjà vu is cryptomnesia, which is where information learned is forgotten but nevertheless stored in the brain, and similar situations invoke the contained knowledge leading to a sense of familiarity. For instance, maybe you went to a park in your childhood, but you forgot about it. When you visit the same park again, you may get the sense of déjà vu.

Conflict Resolution:  When our brain is in a familiar scenario, it can recall memories of the place from the past and guide us. But in an unfamiliar situation, if our brain is too tired to scan the new environment, it registers the new information as familiar and is happy with that. It doesn't bother to investigate any further. This phenomenon may be triggered by a familiar pattern in the new scenario, like a traffic lights, or a zebra crossing for example.

Dreams:  This is perhaps the simplest theory behind déjà vu. The experiences may duplicate the situation depicted in a dream. In a survey by Brown University, 20% of the respondents said that their déjà vu experiences were from dreams.

Despite déjà vu is very common, but we know a little about it. The stated theories are just theories. The déjà vu sensations triggered in lab conditions are artificial and maybe don't replicate the spontaneous déjà vu in real life. Maybe in real life, it is more intriguing. The thing is, we cannot completely rely on these experiments.

Most of us relate déjà vu with memory. If it is caused by an unrecalled memory, then maybe that memory is helping us to predict the future, at least a little bit? 

These memories allow to determine what to do next or how to react to something. Maybe these memories are training us for the near future? I don't know. Maybe time will tell. But you know about déjà vu. After all, you've read this before, haven't you? Or maybe it really is just a glitch in the matrix.