If you’ve ever been going about your day as usual, only to be struck by the sudden feeling that you’ve somehow—however improbably—already experienced what you’re going through, then congratulations: You’ve just experienced déjà vu. You might even know the name for the feeling. But what is déjà vu, really? And what could possibly explain this weird and unsettling experience?
The answer to that question is a lot more complicated than you might think—largely because there’s still so much that we don’t know about it. There are a few different views about what might cause it, though, ranging from the scientific to the absurd. Here’s a brief look at what we’ve learned about déjà vu so far.
Déjà Vu, Defined
Déjà vu is one of those things that can be difficult to adequately describe; however, most people know it when they feel it. It’s a nagging and slightly uncanny sense that you’ve already lived through or experienced something that you’re living through or experiencing now—even if you know that you haven’t. Indeed, “déjà vu” is French for “already seen.”
French philosopher, parapsychologist, and Esperanto enthusiast Émile Boirac coined the phrase in 1876 in a letter to the editor of the French philosophy journal Revue philosophique de la France et de l’etranger. “Without having examined the facts described in the article, I will report on an illusion of memory which, to me, resembles the same type,” Boirac wrote (as translated by the website Third News). He continued:
“It happened when I first saw a monument, a countryside, a person, which made me all of a sudden realize, and in spite of my judgement, I had already seen what I was seeing. Impossible to say where, nor when: the memory, like the sensation of déjà vu, was no less ‘very alive’ and ‘very clear.’ This did not disappear upon reflection, but to the contrary, seems to increase.”
These days, the most widely accepted definition of déjà vu is the one neuropsychiatrist Vernon Neppe proposed in 1979 and codified in his 1983 book The Psychology of Déjà Vu: Have I Been Here Before? According to this definition, déjà vu is “any subjectively inappropriate impression of familiarity of the present experience with an undefined past.”
Research suggests that déjà vu is a common experience for around 67 percent of the population, with instances typically occurring about once a year for each person. The experience of déjà vu is usually fleeting—only a few seconds long—although the non-memories “recalled” during an instance of it might be extraordinarily vivid.
The Science of Déjà Vu
Unfortunately, there’s a lot we still don’t know about how déjà vu works; per How Stuff Works, it’s difficult to study for a variety of reasons, including the fact that “it occurs briefly, unannounced, only in certain people, and has no witnesses or physical manifestations other than the person saying, “Hey, déjà vu!”
But the literature on the subject does offer a few clues. For example, it seems likely that déjà vu is a memory-related phenomenon. As Scientific American pointed out in March of 2020, studies such as one published in the journal Consciousness and Cognition in 2012 seem to suggest that when we “encounter a situation that is similar to an actual memory, but we can’t fully recall that memory… our brain recognizes the similarities between our current experience and one in the past.” In this study, the researchers used the video game The Sims to create virtual reality scenarios of particular spaces, some of which could be spatially mapped on top of one another—that is, something about the spatial setup between scenarios was similar, even if the location depicted was different. They found that participants were more likely to report feeling déjà vu when they saw these scenarios, although they couldn’t necessarily identify where they had seen the set-up before. Per Scientific American, situations like these can leave us with “a feeling of familiarity we can’t quite place.”
Additionally, Akira O’Connor conducted research working out of the University of St. Andrews that suggests that déjà vu may be related specifically to how we check our memories. Using techniques related to trigger false memories, O’Connor’s team was able to induce a sense of déjà vu in the study’s participants. According to O’Connor, as New Scientist put it in 2016, this means it’s possible that when déjà vu occurs, “the frontal regions of the brain are probably checking through our memories, and sending signals if there’s some kind of memory error—a conflict between what we’ve actually experienced and what we think we’ve experienced.”
There may be neurological mechanisms associated with déjà vu as well. For instance, the phenomenon appears to be particularly tied to temporal lobe epilepsy; as a 2012 review of the literature on the subject published in the journal Epilepsy Research and Treatment noted, “clinical reports suggest that many [temporal lobe epilepsy] patients experience the phenomenon [of déjà vu] as a manifestation of simple partial seizures.”
According to The Conversation, some researchers believe that the type of déjà vu associated with this particular condition is different than garden variety déjà vu; for example, it tends to be “enduring” rather than “fleeting.” Again, though, there’s so much we still don’t know about how déjà vu works that it’s difficult to say for certain whether or not there are major differences or similarities at play here.
Other Possible Explanations for Déjà Vu
Of course, depending on how you feel about psychic phenomena, there are other possible explanations for what déjà vu is. It’s perhaps not a coincidence that much of the early research and writing about déjà vu was done by people who were, in addition to their other qualifications—doctor, philosopher, or what have you—parapsychologists, as is the case with both Émile Boirac and Vernon Neppe.
For example, some believe that déjà vu is an echo from a past life you may have lived before. Indeed, according to Brian Weiss, a proponent of past-life regression, déjà vu is “one of the most common signs of a past life.” Those who believe in past lives and reincarnation frequently repeat this idea.
Others believe the feeling to be not a memory of the past, but rather, a sign of the future—that is, that déjà vu is a form of prophecy or precognition. It’s worth noting that scientific research has determined the predictive feeling of déjà vu to be illusory—for example, one study published in 2019 found that it’s actually indicative of a postdictive bias—but many who believe this theory feel quite strongly about it.
Along those same lines, there generally isn’t much—if any—hard science behind these psychical interpretations of déjà vu; however, they remain popular all the same.
The standard experience of déjà vu isn’t the only type out there, by the way. Other related phenomena falling under the same larger umbrella include jamais vu (“never seen”), in which a situation that should be familiar goes unrecognized by the person experiencing it; déjà rêvé (“already dreamed”), the feeling that you’ve previously dreamed something you’re now experiencing; and presque vu (“almost seen”), the experience that a memory is almost within your grasp, but continues to elude recognition.
Research continues—and in the meantime, whenever something feels oddly familiar, we’ll continue to ask ourselves: “Have I already been here before?”