Tjiang W, Ooi SL Amy, See KS Kris
Have you ever experienced a feeling of familiarity while in new place ? Suddenly it seems as if you have been there before. Or maybe you meet someone new, having a conversation and you have a feeling that you have already experienced this before? At the same time, you’re clearly aware that this cannot be a reality because you have never been in this place or met these people at any time in your past.
What exactly is this?
This feeling of familiarity is known as déjà vu. A French term meaning “already seen”. And about two out of three people have experienced the phenomenon at one time or another, according to a 2003 review in the journal Psychological Bulletin.
Déjà vu occurs most often between 15 and 25 years of age and decreases progressively with age. It seems to occur equally among men and women and across races.
Studies have suggested that déjà vu is more common among people from higher socioeconomic groups and more highly educated individuals, people who travel more frequently, when we are particularly tired and stressed, or related to certain drugs may increase the likelihood of experience déjà vu.
A peculiar visual context most often triggers déjà vu, although spoken words alone sometimes create the illusion of familiarity.
The researchers found déjà vu most often occurred when new scenes were very similar to previously experienced scenes in terms of their spatial layout but not similar enough that people consciously recognized the resemblance.
Despite very popular, experiences of déjà vu are poorly understood in scientific terms. Déjà vu occurs briefly, without warning and has no physical manifestations.
It’s a sign of our brain checking its memory. Déjà vu may actually be one sign of a healthy mind that is able to spot familiarity signals that are incorrect. It could also be the result of your brain struggling to process multiple pieces of information, but for some reason, can’t align them correctly. That lack of “synchrony,” might be responsible for that déjà vu feeling.
Aura
In fact, although almost anyone can have an episode of déjà vu every once in a while, more frequent and intense forms of the phenomenon are usually seen in people who have seizures in the temporal lobe, a condition called temporal lobe epilepsy.
Some people who have temporal lobe epilepsy experience an aura (a warning of sorts) of déjà vu right before they have a seizure. This tells us that déjà vu is probably linked to the temporal lobe of the brain. In people who do not have epilepsy, déjà vu could be a mini-seizure in the temporal lobe, but one that does not cause any other problems because it stops before it goes too far. This links back to the idea that déjà vu might be caused by a strong feeling of familiarity. The familiarity is signaled by brain cells in the temporal lobe, but is noticed and ignored by another part of the brain that checks whether all the signals coming to it make sense. The part of the brain that does this checking may well be in the frontal lobe. We know the frontal lobe is important for making decisions. Because déjà vu is such a fleeting event, most occurrences last no longer than a matter of seconds. It is frustratingly difficult to study.
Déjà vu may be related to some other phenomena that are equally challenging for scientists to explain. Jamais vu, or "never seen," occurs when a person experiences something familiar, like their own living room but feels that they've never been there before. And Déjà entendu ("already heard") occurs when someone is certain they've heard something before, like a snippet of conversation or a musical phrase, but cannot recall the precise time or place.
Regardless of what’s happening or what’s causing it, for the vast majority of people, déjà vu is pretty harmless. Unless you’re experiencing an epileptic seizure.
References
1. Chauvel P. Deja Vu: What It Is, When It May Be Cause for Concern. Health Essentials. 2017
2. Choi CQ. Been There, Done That or Did I? : Déjà Vu Found to Originate in Similar Scenes. Scientific American. 2012
3. Hamzelou J. Mystery of Déjà vu Explained : It’s how we check our memories. New Scientist. 2016
4. Lallanilla M. What Is Déjà Vu?. Live Science. 2013
5. Masters M. 3 Reasons You Sometimes Have Déjà Vu, According to Science. Health. 2016
6. Newman T. Déjà vu: Re-experiencing the Unexperienced. Medical News Today. 2017
7. Reichelt A. Explainer: What is Déjà vu and Why does it happen?. The Conversation. 2013
8. Teale JC, O’Connor AR. What is Déjà vu?. Frontiers for Young Minds. 2015
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