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What is Déjà Vu..? What is Déjà Vu..?

VO: Noah Baum WRITTEN BY: Caitlin Johnson
Ever get the feeling that you've been here before? That this exact thing has already happened? Déjà vu is the confusing cognitive sensation in which life seems to be repeating itself. But, what's really going on in your brain? Are you really repeating memories? Is it just a mental glitch? Or something much more significant?

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What is Déjà Vu?

If you’ve ever vividly had the sensation wherein what you’re experiencing right now feels as though it has already happened, that’s the phenomenon known as “déjà vu”. Meaning ‘already seen’ in French, it truly is one of life’s little mysteries, and a concrete explanation of its exact cause – or even of precisely what it is – still eludes us. We do know that it happens most commonly to people aged between 15 and 25, and then tends to get less frequent. But, it rarely happens to children at all until they reach around age 10, and even those rules aren’t set in stone. Neurologists, psychologists, and other researchers have speculated that it may all be to do with individual brain development – but that’s just one theory of many. So, what are the others?

One of the most common explanations for déjà vu is that there’s a desynchronization in our brain processes and the way the five senses are interpreted in our minds. This means that our sense of sight and sense of hearing, for example, become out-of-sync. When the senses catch up with each other – after a difference far too small to actually perceive – that’s déjà vu. It’s something we’ve already partially experienced which therefore seems familiar. Another similar theory suggests that an attention deficit is responsible. As in, if we’re not paying full attention to our surroundings, even when we believe that we are, our subconscious return to awareness will cause us to think we’re experiencing something twice.

Despite the apparent elusiveness of déjà vu, there has been a lot of physiological research into it. And there are some other things we know for certain. For example, it’s definitely linked to the temporal lobes of our brains. It’s also much more common in people with epilepsy, and for sufferers of severe epilepsy it can even make it difficult to discern what’s real and what’s not – the fairly frightening reality of déjà vécu involves a sense that entire sequences have been lived before. We know that déjà vu is experienced as an “aura”, which is a recognised precursor to an epileptic seizure – although not all seizures come with prior warning.

The experience is also common in people with damage to the temporal lobe, and we know that by electrically stimulating this region of our brains déjà vu can be artificially triggered. This doesn’t mean that everybody who’s ever had déjà vu has some sort of brain damage or a neurological disorder, especially considering that it happens at least once to an estimated 60-80% of people. However, some have suggested that déjà vu could potentially be a minor epileptic event. You don’t need to have epilepsy to suffer a mild instance of it – and that’s what this sensation is.

The history of epilepsy treatment has thrown up other potential answers, too. Harrowingly, an epileptic patient named Henry Molaison – also known as “Patient H.M.” – had an experimental lobotomy to remove much of his temporal lobe in 1953. The surgery did mitigate his epilepsy, proving the importance of that region of the brain to the condition… But his life was irreparably ruined as he was left completely unable to form new memories. This happened because located in the temporal lobe is the hippocampus – or the hippocampi, since we have two. And here we find another hotspot for déjà vu theory.

This tiny piece of brain plays an enormous role in our memory. So, rather than explaining it away as some kind of seizure, some say that déjà vu is in fact a botched memory process. The hippocampi are responsible for, among other things, transferring memories from “short-term” to “long-term”, and “saving” them. It could be that déjà vu is when the brain makes a mistake, and instead of some information going to our short-term memory, it’s “saved” immediately to the long-term. As such, the brain is accidentally tricked into thinking that something which just happened (or is still happening) actually occurred a long time ago. Because this is wrong, the new, erroneously long-term memory is incredibly detailed, much more than we’re used to for standard long-term memories. So, naturally, when we recollect it we’re subconsciously surprised by just how vivid it is. And, according to this particular interpretation, it’s that surprise which is déjà vu.

There are more memory theories than just that one, however. Previously it was taken as fact that déjà vu is the brain creating false memories. False memories are notoriously tricky, though specialist, Valerie F. Reyna, has suggested that they are a “memory dissociation”, where we cannot determine if we actually did experience something, dream it, or if it’s simply an anomaly. The false memory explanation has lost traction recently, but a final contemporary theory suggests another relationship between memory processes and déjà vu: arguing that it may instead be a sign that our brain is checking our memory. A complex study – conducted by a team from the University of St Andrews, in 2016 – used a series of trick questions and an MRI scanner to examine the cognitive functions of 21 volunteers. It discovered that déjà vu could actually be the sign of a healthy brain, capable of spotting memory mistakes, as the eerie sense of having done something twice is actually us determining what’s true and what’s not. So, a few incidents of déjà vu here and there aren’t anything to worry about.

Interestingly, déjà vu isn’t the only phenomenon like this. There’s something equally as bizarre that most people have also experienced called a “hypnic jerk”. This is when you’re drifting off to sleep but suddenly feel as though you’re falling, and so you wake yourself up. These muscle spasms could also be a result of epilepsy, as similar spasms – called epileptic myoclonus – happen as seizure auras. But, just like déjà vu, hypnic jerks happen to everybody and often for seemingly no reason whatsoever (though they are at times associated with anxiety and stress).

There’s also “presque vu,” “jamais vu,” and “déjà rêve,” which mean “almost seen,” “never seen,” and “already dreamed” respectively. Yet again, the majority of people will have experienced all of these. “Presque vu” is best described as the tip-of-the-tongue feeling, when you’re on the precipice of remembering a certain word or a moment of realisation. Usually, “presque vu” can be solved by simply going away and doing something else, as it’s just a temporary block. “Jamais vu” is the name for what happens when you say a word over and over and over again until it loses its meaning – another cognitive trick.

Finally, “déjà rêve” is arguably the most intriguing, as it is often confused with déjà vu. It relates to an intense feeling that you’ve already had a dream about whatever’s happening to you in the present. Those that subscribe to a paranormal explanation for déjà vu (and similar experiences) often suggest that they are, in fact, the result of precognitive dreams. So, as per this theory, déjà vu really does imbue its subject with something of the psychic. Even stranger, there have been multiple studies yielding reports of people having apparently dreamt the future in some way.

There’s currently no way to conclusively know which, if any, of these theories are true. There may be even more factors at work than we’re currently aware of and it could take decades more research to truly determine what déjà vu is, especially since there’s at least some evidence to support every idea – even dreaming the future. The whole thing could be much more or much less complicated than we think; or maybe, somewhere out there, everything really has already happened once before?

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