“Déjà vu”: when you have the impression of reliving the same event twice

Many of us have experienced deja vu, but none seem to know why. Even someone with their feet firmly planted in the realm of logic and science can’t help but feel a bit esoteric when deja vu hits, like a whimsical jolt of nostalgia from the depths of the ether. . Deja vu has fascinated researchers and laypersons alike for centuries. The experience is also relatively widespread. According to various surveys, almost two-thirds of people have experienced this feeling of backwardness.

However, despite the prevalence of deja vu, it has proven to be a tricky phenomenon to pin down. You can’t just lay someone in an MRI scanner and wait for an episode, because they could be there for weeks.

Although a definitive answer has not been given, there are a whole host of theories that drift between the fields of psychology and neuroscience. We’ll explain some of the more compelling theories here.

What we know about deja vu

While it’s considered inappropriate to prematurely alert readers to an article’s conclusions, we still don’t know why or how deja vu occurs. So what do we know from experience?

– Age: deja vu seems to occur more frequently in young people, and becomes less and less frequent with age.

– Sex: Men and women seem to feel it about the same frequency.

– Social: According to some studies, deja vu is more common in people from higher socioeconomic groups and in more educated people.

– Travel: People who travel more frequently are more likely to experience deja vu. A 1967 study found that only 11% of people who had never traveled had seen, compared with 41% of those who made between one and four trips a year and 44% of those who traveled five or more times a year.

– Stress: Other studies have shown that deja vu is more common when we are particularly tired, stressed, or both. For example, there are many reports of troops experiencing feelings of deja vu as a battle approaches.

– Drugs: Certain drugs can increase the likelihood of a feeling of deja vu. A case study published in 2001 chronicles the experience of a 39-year-old man, in good mental health, who experienced a recurring feeling of deja vu when he took amantadine and phenylpropanolamine at the same time. to treat the flu.

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Where does deja vu occur in the brain?

Perhaps surprisingly, deja vu does not seem to correlate with particular mental disorders. The only condition that is reliably associated with this experience is temporal lobe epilepsy (TLE).

The temporal lobe seems to be important in deja vu. In this particular form of epilepsy, as in other types, there is often an “aura” before a seizure. In some people with epilepsy, the aura regularly contains deja vu. The temporal lobes, involved in visual memory and the processing of sensory data, seem to be the main suspects for the existence of a feeling of deja vu.

A study carried out in 2012 made it possible to refine the research a little more. They found that stimulation of the entorhinal cortices (ECs) can produce deja vu-like experiences. ECs, located in the medial temporal lobe, play a role in spatial memory and memory consolidation.

4 theories to explain the “déjà vu”

The region of the brain associated with deja vu may be stuck, but what causes it? In general, deja vu theories fall into four categories:

– double treatment
– neurological
– memory
– attentive

None of the following theories holds all the answers, but each provides a unique opportunity to revel in the thin but remarkably solid experience we call consciousness.

1 Dual treatment

In short, dual processing theories suggest that two cognitive processes that normally operate in parallel are, for a moment, decoupled. This category of explanations can be divided into four types, depending on the processes one imagines to have decoupled. It should be noted that these are some of the oldest deja vu theories, and none of them are based on empirical evidence. However, they give food for thought:

Knowledge and recall:

This theory holds that familiarity and retrieval are two cognitive functions that normally work in concert. If for some reason the familiarity was triggered by mistake, we would feel unfounded that we had already been somewhere.

2 Encoding and recovery

This explanation is accompanied by a practical metaphor: a tape recorder. Normally, a tape recorder’s recording (encoding) head and playback (retrieval) heads operate separately. Either we drop the memory or we retrieve it. The theory goes that sometimes the two heads can accidentally work together. This means that we generate a false sense of familiarity with the sequence of events that is playing at the same time. Although the metaphor is pleasing, scientists are not convinced. Memory formation and retrieval does not work that way.

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3 Perception and memory

This theory states that when we perceive events, memories are formed at the same time. Normally, we focus on perceiving events, but if we are tired or distracted, memory formation can occur at exactly the same time we perceive our surroundings. In this way, our perception of the “now” would appear as a memory.

4 Double consciousness

First envisioned in the 1880s by Hughlings-Jackson, it posits that we have two parallel streams of consciousness: one monitoring the outer world and the other our inner daydreams. If the primary, more sensitive, outward-looking consciousness wanes due to fatigue, the more primitive consciousness would take over and accidentally confuse the new experiences with the old internal experiences.

While each of the above is food for thought, none of them live up to modern scientific theories.

Neurological explanations

Neurological explanations for deja vu are generally divided into “attack” and “neural transmission delay”.

1 Crisis

As mentioned earlier, people with epilepsy often experience a sense of deja vu as part of the aura before a seizure. Logic dictates that if this is the case, deja vu is a minor type of crisis. However, the data does not confirm this. Deja vu is not more common in people with epilepsy in general, and people who have deja vu more regularly are not more prone to seizures.

Also, although the connection between deja vu and epilepsy is well established, the majority of people with this disorder do not experience deja vu as part of their aura.

2 Neural transmission delay

There are several versions of this theory. One describes deja vu as information that travels from the eye through a number of pathways to the higher centers. If information from two paths arrives at different times, for some reason, the brain may perceive the second message as old information.

Memory Explanations

This section of theories focuses on how memories are stored, preserved, and retrieved. A memory-based explanation has some experimental basis. A 2012 study, using virtual reality, provided some intriguing insight. The researchers found that if participants were shown a scene that was very similar to a scene they had been shown before but did not remember, sometimes a sense of deja vu was felt.

In other words, if the memory of a scene is not recalled to us when we watch a new similar scene, the previously experienced scene stored in our memory bank still exerts some influence. Perhaps a feeling of familiarity.

Memory Dysfunction Explains Deja Vu

Another advanced memory theory overturns our notion of familiarity. Perhaps we have thought of “familiarity” incorrectly. For example, if we saw our postman at the front door of our house, a very familiar scene, it would not produce a feeling of familiarity. On the other hand, if we saw our postman out of the blue, for example if we are on holiday out of town, it would evoke a feeling of familiarity.

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Our so-called sense of familiarity doesn’t strike when we see familiar things. If that were the case, we would almost constantly feel a sense of familiarity. Rather, this feeling of familiarity occurs when we see something unexpectedly familiar.

When we see something familiar, our brain processes it faster and it takes less effort. If we were to see something very familiar (but don’t recognize it at the time) in an unfamiliar setting, the familiar item would be processed quickly (even if we didn’t notice it), resulting in a feeling of familiarity to the whole scene.

Careful explanations

The fourth part of the explanations of deja vu concerns attention. These theories are based on the fact that a scene is briefly observed without paying due attention to it. Then, shortly after, the same scene is perceived again, but this time with complete perception. The second perception matches the first and is accidentally assumed to be older than it actually is, triggering a sense of deja vu.

More to learn

As intriguing as these theories are, none have been proven and, in fact, all of them might have some, if any, truth. We assume that deja vu is a unique type of experience, but it could be generated in subtly different ways, either between individuals or within the same individual at different times. Although the temporal lobes seem to be involved, we are really no further along in understanding the reasons for this pervasive and disturbing phenomenon. So the next time you’re feeling deja vu, be sure to revel in one of the most fascinating unexplained mysteries in human biology.




* Presse Santé strives to transmit medical knowledge in a language accessible to all. In NO CASE can the information given replace medical advice.

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