Have you ever felt like you’d been to a place before when you were there for the very first time? How about a conversation or a person for that matter?

This feeling of familiarity is, of course, known as Déjà vu (a French term meaning “already seen”). It is believed that it happens to at least a good 60% to 80% of people occasionally. It’s an experience that’s fleeting (most of the time) and it occurs at random. Here are some reason of Déjà vu.

Now the question is why does it happen?

Popular culture does cover Déjà vu but the concept is hardly understood in scientific terminology. Déjà vu occurs briefly, without warning and has no physical manifestations other than the announcement: “I just had Déjà vu!”

It is the opinion of many a researchers that the phenomenon is a memory-based experience and memory centres of the brain are responsible for it.

1. Memory systems

Memory systems
Memory systems

The medial temporal lobes are vital for the retention of long-term memories of events and facts. Certain regions of the medial temporal lobes are important in the detection of familiarity, or recognition, as opposed to the detailed recollection of specific events.

It is also largely believed that familiarity detection depends on rhinal  cortex recollection is linked to the hippocampus.

The randomness of Déjà vu experiences in healthy individuals makes it difficult to study in an empirical manner. Any such research is reliant on self-reporting from the people involved.

2. Glitches in the matrix

Glitches in the matrix
Glitches in the matrix

A subset of epilepsy patients consistently experience Déjà vu at the onset of a seizure – that is, when seizures begin in the medial temporal lobe. This has given researchers a more experimentally controlled way of studying Déjà vu.

Electrical disturbance of this neural system generates an aura (a warning of sorts) of Déjà vu prior epileptic event.

If you measure these neuronal discharges in the brains of these patients, scientists have been able to identify the regions of the brain where Déjà vu signals begin.

It has been proposed that Déjà vu could be triggered by a similar neurological discharge, resulting in a strange sense of familiarity.

However, there’s a big chunk of of Déjà vu experienced by temporal lobe epilepsy patients is different from typical Déjà vu.

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4. Mismatches and short circuits

Mismatches and short circuits
Mismatches and short circuits

Now the difference follows.

This information basically bypasses short-term memory and instead reaches long-term memory. This implies Déjà vu is evoked by a mismatch between the sensory input and memory-recalling output. This explains why a new experience can feel familiar, but not as tangible as a fully recalled memory.

So far there is no simple explanation as to why Déjà vu occurs, but advances in neuroimaging techniques may aid our understanding of memory and the tricks our minds seem to play on us.

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