Déjà vu, French for ‘already seen’ is one of the least understood sensations the brain is capable of letting us experience. This is because it is hard to catch one in progress. Lying down on an MRI scanner in the hopes of recording one would perhaps yield unsatisfactory results even after weeks. The phenomenon however, is widely experienced, with two thirds of the population having experienced it. It momentarily jolts the victim off of the axis of logic as we try to discern reality from tricks of the brain.

What is known about déjà vu


Instead of focusing on what is unknown, there are known facts about déjà vu. Occurring in equal amounts for men and women, déjà vu tends to be experienced more by the younger population. This tallies with a 2012 study done by researchers in the UK, which concludes that déjà vu results from the brain trying to check itself. As memory declines with age, so does the general checking system. Concurrently, déjà vu is less felt, as the chance to spot memory mistakes is less.

In addition, déjà vu is more likely to be experienced by people of a higher social class and with a more educated background. People who frequently travel are also more likely to be subjected to déjà vu than those who do not travel. A 1968 study showed that 44% of the people who experienced déjà vu were frequent travellers, versus only 11% experiencing it who did not travel. Moreover, having being under stress and fatigue will more likely trigger a bout of déjà vu, as it is likely when being under the influence of certain drugs.


Déjà vu, a non-medical condition


Until proven otherwise, déjà vu remains to be a non-medical condition. It is however somewhat associated with temporal lobe epilepsy (TLE), where the brain’s temporal lobe comes into play. The entorhinal cortices, located in the temporal lobe, is responsible for spatial memory and memory consolidation. A TLE patient might sometimes experience an aura prior to the seizure. The aura is a minor foreshock, lasting up to a couple of minutes preluding to the actual seizure.

It is this aura that has been linked with déjà vu-like feelings. An English neurologist, John Hughlings Jackson, pioneered the aura discovery in 1898, noting that epileptic auras involve vivid memory-like hallucinations and going back and forth between scenes – déjà vu. One would argue that déjà vu is therefore a mini seizure.

However, little claim can attest to this. People who experience déjà vu are not at all prone to seizures, as well as people with TLE are not more prone to having déjà vu as part of their aura.

Déjà vu all over again


As preluded, the 2012 study had gathered its conclusion through triggering of the feeling of déjà vu. The researchers used a technique of triggering false memories, where one specific word was not told but the related words told suggested that the specific word had been told. Thus, falsely triggering a feeling of déjà vu. Surprisingly, the part of the brain associated with memories was not in play. Instead, it was the frontal lobe where decision-making takes place that was active. This suggests that déjà vu is a sign that the memory checking system is working well.

There are many theories as to why déjà vu happens, none of which have been determined as the sole reason, mainly due to lack of data backing it up. Generally, theories ranging from neural transmissions delay to dual consciousness minding the body at the same time all have flaws and don’t hold much water over time. However, the theories do serve as food for thought to demystify this biological mystery. MIMS

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Sources:
http://www.medicalnewstoday.com/articles/317895.php
https://www.newscientist.com/article/2101089-mystery-of-deja-vu-explained-its-how-we-check-our-memories/
http://www.independent.co.uk/news/long_reads/d-j-vu-extreme-memory-brain-health-biology-personal-experience-a7769741.html
https://medicalxpress.com/news/2012-05-scientists-uncover-deja-vu-mystery.html
https://www.psychologytoday.com/blog/brain-babble/201208/the-neuroscience-d-j-vu