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What Exactly Is Déjà Vu, And What Causes It? Types Of Déjà Vu

The film Groundhog day, released in 1998, is set in the town of Woodstock - and tells the story of Bill Murray’s character Phil Connors, who repeatedly relives February 2nd.

What Is Déjà Vu?

Chances are that like good old Bill Murray - you’ve had that strange feeling where you feel like you’ve already experienced a situation before, even though you know you haven’t. That sensation, of course, is déjà vu, and between 60% to 80% of us will experience it at some point in our lives. But what exactly is déjà vu, and what causes it?

What Exactly Is Déjà Vu, And What Causes It?

Well, according to professor of psychological science James Michael Lampinen, déjà vu is “a strong sense of global familiarity that occurs in a seemingly novel situation.” It’s that little nagging voice in your head saying “I’ve been here before” when you know that’s not the case. You feel you’re eating cheese straight out of the fridge at 2am – we know it’s not the first time.

The phenomenon was first named by French parapsychologist Émile Boirac in 1876. The name itself is fairly self-explanatory—déjà vu means “already seen” in French. But why was it a parapsychologist - someone who studies psychic phenomena - who was so interested in it?

Well at the time, déjà vu was considered so strange it was thought to be something supernatural, much like clairvoyance or mediumship. For many years, it was considered an area unworthy of study, most often explained away as a side effect of reincarnation or possibly even alien abduction.

Never been in this room before that somehow feels so familiar? Well then, you must have been here in a past life, obviously! Either that or aliens vigorously probed you on this very spot before wiping your brain.

But over the years, the scientific community has begun to take déjà vu more seriously - though the same can’t be said for the general public - a 1991 Gallup poll of attitudes towards déjà vu saw it placed alongside astrology, paranormal activity, and ghosts—you know, the holy trinity of ridiculous superstitious beliefs.

Types Of Déjà Vu

The name déjà vu itself has become a catchall term for unexpected familiarity, but there are actually several different varieties of the phenomenon to remember. 

Déjà entendu

Déjà entendu means "already heard" in French. It is the sense you’ve already heard something that’s in fact new to you –  heard something even if the details are unclear or even imaginary. 

Déjà Nintendo

Not to be confused Déjà entendu with Déjà Nintendo, which is when you suddenly remember you’ve been playing Pokemon for six days straight and need to get a life.

Déjà pensé

There’s also, déjà pensé, the feeling you’ve had a particular thought before when in reality you haven’t.

Déjà gouté 

Déjà gouté relates to food, Déjà gouté means "already tasted" in french. In this case, you feel you already tasted something.

Déjà voulu

Déjà voulu is the sense you’ve desired something - or someone - before when you haven’t.

It’s important to note that déjà vu is completely different from precognition, which is where people have the feeling they know what’s about to happen. That’s not déjà vu as much as it claims to be psychic and mental.

To be on the safe side, psychologists have actually tested this out. Back in the 1950s, when scientists had free rein to attach whatever they felt like to people’s brains, direct stimulation of the frontal cortex, which induced déjà vu, was found to also produce the feeling of premonition—but without granting any actual power to predict things or see the future in any way. And more recent, less brain-proby experiments have found exactly the same thing.

These days, we separate déjà vu into two distinct types:

The first, what we’d consider “regular” déjà vu, is seemingly random.

The second is associated with neurological conditions like temporal lobe epilepsy.

Pathological déjà vu

This latter form is usually accompanied by other symptoms and is termed pathological déjà vu. It’s caused by disease or injury of some kind, particularly damage to or malfunction of the frontal lobe, the part of the brain that handles memory. Pathological déjà vu is easier to study, since it occurs far more frequently in the individuals it affects, and researchers have been able to identify the areas of the brain where the feeling originates. But pathological déjà vu is generally considered to be a little bit different from your normal everyday déjà vu. For instance, those suffering from this condition may actually think they’ve been in a given situation before for sustained periods of time, rather than merely experiencing a fleeting feeling.

A British man, Pat Long, suffered from one of the worst cases of déjà vu on record. In his mid-thirties, Pat was diagnosed with a brain tumor the size of a lemon after suffering epileptic seizures. To most of us, déjà vu is nothing more than a strange moment, a kind of ‘huh, that’s weird', that lasts no more than a second or two. Pat’s déjà vu was something else entirely.

Déjà vecu

In fact, it wasn’t really déjà vu at all, but déjà vecu, meaning ‘already lived’ as the name suggests, Pat’s déjà vecu meant he would believe he had lived whole sequences of events before. The feeling was so strong and would last so long that for weeks on end he would be almost entirely unable to differentiate between past experiences and the present, with memories, hallucinations, and the products of his own imagination all interchangeable to him.

Jamais vu

Epilepsy sufferers often experience bouts of déjà vu during seizures, as well as the experience described as the opposite of déjà vu - jamais vu - Meaning “never seen”. Jamais vu is when a situation that should be familiar instead feels foreign for some reason as if you’re experiencing it for the first time. While not quite so famous as its cousin déjà vu, jamais vu is easier to induce—repeat any word aloud enough times in a short space of time and it will slowly start to lose its meaning.

Inducing déjà vu is far more difficult, which means studying the sensation can be tricky - that’s part of the reason we still don’t know exactly how it works or what causes it. For most of us, it’s not a daily occurrence, so getting data on a significant scale in a lab setting is difficult. Difficult, but not impossible.

As part of a 2006 study, scientists at Leeds Memory Group used hypnosis in an attempt to induce déjà vu. They theorized the sensation was caused by a kind of malfunction in memory processing. When the human brain is presented with a new scene, it carries out an internal check to see whether elements of the scene have been observed before. If they have, a different part of the brain identifies the scene as familiar. The researchers hypothesized that déjà vu occurs when the second part of this process is triggered without the first, and they were able to successfully use hypnosis to artificially trigger the malfunction simply by telling hypnotized participants that the next time they saw a particular word, the would know it was familiar but not know where they’d last seen it.

Did That Explain The Mystery?

Well, not necessarily, because other researchers attempting to recreate déjà vu have come to their own, sometimes very different conclusions.

According to a 2014 study conducted at the University of St Andrews in Scotland, déjà vu may actually be a healthy and important neurological failsafe that performs a conflict resolution function to prevent false memories from forming. As part of the experiment, researchers used word association techniques to convince participants they’d been shown certain words they hadn’t, effectively forming simple ‘false memories. When later quizzed on these memories, around two-thirds of participants reported experiencing déjà vu. Interestingly, MRI scans of their brains showed activity not in the hippocampus, which is responsible for memory, but in the frontal cortex, which is responsible for decision-making.

The researchers theorized that déjà vu was experienced as the brain attempted to resolve the conflict between what the participants had actually seen, and what they thought they’d seen. As interesting as these ingenious lab-based explorations of déjà vu are, it’s also possible there’s a much simpler explanation to all this - that déjà vu is simply triggered by a ‘forgotten’ memory. After all, it’s well established that less important and infrequently accessed memories are eventually forgotten, or at least suppressed to some extent. Déjà vu may just be the feeling we get when something we’re experiencing is similar to one of these discarded memories that’s gone but not-quite-forgotten.

Frequent travelers are also thought to experience déjà vu more regularly than others, which perhaps supports this theory - the more places you’ve been and the more different things you’ve seen and done, the more likely it is that a seemingly new experience might feel familiar to you because it’s similar to something you no longer quite remember - consciously, at least.

We can’t talk about Déjà vu without giving a quick shout-out to Sigmund Freud, who believed the phenomenon was caused by repressed desires or old traumatic memories because that guy linked everything to repressed desires and trauma. He also had a suspicion that regular suffers of déjà vu were most likely fixated with their mother’s genitals, but let’s face it, Freud wasn’t happy until he’d gotten at least one set of genitals into each of his theories.

Freud reasoned that your mother’s ‘secret garden’ is the only place in the world every single one of us has been in just once before. Whether or not people born by caesarian section experience déjà vu is, so far as I’m aware, unknown.

Dual Processing

Another older explanation, albeit one that remains a valid theory today, is known as Dual Processing. It suggests our experiences are handled in both hemispheres of the brain, and any delay in processing from one side may cause that eerie feeling of déjà vu.

This was tested by Robert Efron in 1963, and he found that the temporal lobe of the brain’s left hemisphere is where incoming information is sorted. But he also found that the temporal lobe receives this information both directly and after a short detour through the right hemisphere of the brain. If, for any reason, the information traveling through the right hemisphere is delayed at all, it could be assigned the wrong timestamp, giving a feeling of familiarity we assume is from long ago, but is in reality from mere moments before.

Divided Attention

This idea that déjà vu may actually be a sense of familiarity from extremely recent events rather than past ones underpins another possible cause of the phenomenon - Divided Attention. The idea here is that when your attention is split as you experience a new situation- for example if you’re talking to a friend as you enter a pub for the first time - it may be that you take in your surroundings subliminally without really paying attention to them. In essence, you’re subconsciously observing the situation faster than you consciously process it. The gap between the completion times of these two processes isn’t noticeable enough that you’d suddenly pause like a robot without a command……but it is enough to think you’d experienced the event before, since, as in the dual processing theory, you kind of already have, fractions of a second ago.

To test this, Marsh and Brown showed groups of students photographs of various locations and asked them if they were familiar. Unbeknownst to the students, some of the images had been flashed onto the screen just before for a very short time, only 10 to 20 milliseconds, which was long enough for the student's brains to pick up on the images, but not long enough to consciously notice them.

As expected, the locations that had flashed up, like those creepy transition shots in The Ring had wormed its way into the students’ subconscious and were recognised as familiar, even though the students had never been to any of them.

Whichever theory you like the sound of, the truth is they’re all still just that - theories. Despite science’s best efforts, we still don’t know for sure what causes déjà vu.

One of the latest studies, published in 2019, found that people who experienced déjà vu more frequently used different parts of their brain to retrieve memories than people who rarely or never do. In particular, frequent déjà vu-ers—showed less activity in their hippocampi, the so-called librarians of the brain that help consolidate memories, suggesting that people who don’t get déjà vu may simply be those with better memories.

Equally, if you consider the fact that déjà vu is most prevalent in people between 15 and 25 years old, perhaps it’s just a sign that we’re not senile yet and can still tell real memories from fake ones—a comforting thought for anyone in that age bracket, and a sobering one for all of us over the threshold.

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