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What's Really Happening When You Experience Déjà Vu?

The study of déjà vu is now legit science, though researchers still don’t know what exactly causes it.

By Avery Hurt
Jun 18, 2021 9:00 PM
Glitch effect
(Credit: Ray Bond/Shutterstock)


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If you have the peculiar feeling you've read this before, don't be alarmed. It's probably just déjà vu. Déjà vu is the peculiar feeling that you’ve experienced something before, while at the same time knowing that you haven’t. You visit a friend’s apartment and have the overwhelming sense you’ve been here before, but that can’t be the case. This is the first time you’ve ever visited this city. Still, the feeling may be so intense — and so real — that you almost know what you’ll find when you walk into the kitchen. Experts estimate roughly two out of three people have had the experience at least once.

The French term déjà vu, which translates into English as “already seen,” was coined in 1876 by French philosopher and psychical researcher Émile Boirac. But people had the experience long before it had a name. Over the centuries, humans often took déjà vu as evidence of what they already believed. Sigmund Freud looked at déjà vu and saw repressed desires. Carl Jung thought the experience was related to the collective unconscious. Plato described something similar to déjà vu as evidence of past lives. And of course, there’s the modern Hollywood-hatched idea that déjà vu results from a glitch in the Matrix. It’s not hard to understand why déjà vu got a reputation for being a little woo-woo and supernatural.

Legitimizing the Phenomenon

In 2003, psychologist Alan Brown published a paper in the journal Psychological Bulletin that reviewed what little was known about déjà vu and connected that information to the existing paradigms in cognitive psychology and memory research. In essence, his groundwork set the stage for the research community to take a closer look at the phenomenon in the years to come. Since then, he and a handful of researchers have ushered the study of déjà vu into mainstream science.

In addition to the paranormal associations, déjà vu has presented another hurdle for researchers. The experience typically lasts no more than a few seconds and there’s no warning of when it’s about to happen, making it extremely difficult to study. Much that is known about déjà vu is based on surveys. Still, researchers have come up with novel ways to study it in the wild.

In 2006, a team in England hypnotized subjects to induce déjà vu. Anne Cleary, professor of cognitive psychology and memory researcher at Colorado State University, had a more high-tech idea. She used virtual reality to trigger déjà vu. Cleary and her team took subjects through a series of scenes in the Sims video game, carefully designed so that the spatial layout of one scene was similar to another, even though the actual images were quite different. The subjects experienced déjà vu when a scene was similar to one they’d seen before, indicating that a similarity in spatial layout between two places might lead to a déjà vu-like sense of familiarity in a novel place.

Plenty of Theories

Once déjà vu research was taken seriously, lots of theories began to emerge about what goes on in the brain during a déjà vu experience. One hypothesis is that déjà vu is a problem with memory. This would be a situation where you experienced something, but cannot consciously recall it. When you come across something similar, you recognize the familiarity but can’t call up the memory. So, in the scenario at your friend’s apartment, the space seems intensely familiar because you have been in a very similar apartment before; you just don’t remember it. This view is supported by Cleary’s VR experiments. In the case of her research, it’s the spatial similarity, rather than any specific details, that triggers the feeling of familiarity.

Another popular theory is that déjà vu is caused by a timing mismatch or interruption to your ongoing stream of processing of a current situation. Imagine you were walking down the street and passed a new coffee shop. You glanced at the shop, but about that time got a text and looked away, so you didn’t fully register it. The information was processed at some level, just not fully. When you look up and see the coffee shop, you have the weird feeling that you’ve seen it before — because you just did, even though you have no conscious memory of it.

Another theory is that déjà vu is caused by mini seizures. People with epilepsy are known to have frequent déjà vu experiences. It’s possible that déjà vu in people without epilepsy is caused by some kind of seizure-like activity as well. The brain just misfires a little and that causes the sensation. This fits well with the fact that teenagers and young adults have déjà vu more frequently than older people. The brain is busy rewiring itself in these years making the chances of glitches higher.

Cleary points out that these are not necessarily competing theories. “There may be many different reasons that could all be true for why déjà vu can happen,” she says. 

Not Just Déjà Vu

Though no one has yet pinpointed what causes déjà vu, it’s a good thing that science finally got serious about studying the strange phenomenon. “I think [déjà vu research] has been shedding light on processes that are helping us to understand memory better at a broader level than just trying to understand déjà vu,” says Cleary. Cleary’s lab is currently looking into the connection between déjà vu and seizures, updating their VR techniques and trying to learn more about individual differences in déjà vu experiences.

Whatever déjà vu is, it’s more likely a glitch in memory that a glitch in the Matrix. By investigating that glitch, déjà vu researchers may learn a lot more about how the brain processes memories.

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