What Is Déjà Vu?

A few days ago, I was visiting a new coffee shop in an unfamiliar neighborhood. In line to place my order, a polite stranger in front turned around, nodded at me, and said, "Hello." In that otherwise mundane moment, I felt an overwhelming sense that I had been there before, that I'd even lived that very moment before, despite knowing that this wasn't possible.

I'd just experienced yet another episode of déjà vu.

What is déjà vu?

Déjà vu is the eerie sense that you're currently experiencing something that you have experienced before. It's a sensation that a place, person, or event is strangely familiar to us. This sensation of familiarity is coupled with the awareness that this familiarity is incorrect.

The ancient philosopher St. Augustine was the first person to refer to the concept of déjà vu in 400 A.D., when he called the sensation “false memoriae.” The French philosopher Emile Boirac was the first to use the term "déjà vu" in 1890. Then the neurologist F. L. Arnaud was the first to use the phrase in a scientific context at an 1896 meeting of the Societe Medico-Psychologique, and from there, it became incorporated into our everyday language.

Déjà vu is very common. Studies show that upwards of 97 percent of people are thought to have experienced déjà vu at least once, with more than two-thirds of people experiencing it with some regularity. Déjà vu is most common in the age bracket of 15-25, and its frequency decreases as we age.

Déjà vu is French for "already seen." The phenomenon has a mysterious counterpart—"jamais vu," meaning "never seen." This is the rarer experience of someone being unfamiliar with their situation, despite rationally knowing that they have been in the situation before. It's commonly explained as when someone momentarily doesn't recognize a word, person, or place that they know, for example, when someone walks through their own neighborhood but fails to recognize where they are. A cousin to these phenomena is "presque vu," meaning "almost seen." This is the failure to remember something, but with the sense that recall is imminent, like forgetting a name but feeling the answer is "on the tip of their tongue."

How does déjà vu happen?

In the movie The Matrix, Neo experiences a déjà vu moment when a black cat walks by him twice in the same way, indicating a "glitch in the matrix."

Some people have supernatural explanations for déjà vu. As an eerie sense that a moment is somehow being relived, some believe that déjà vu is proof of paranormal phenomena, like psychic dreams or past lives. There are religious perspectives too, in which déjà vu is seen as evidence for reincarnation; the belief in Hinduism, Buddhism, and other religions that after death one is reborn in one or more successive existences.

But there are more scientific explanations for the experience, too. Recent research has shown that déjà vu may be a matter of perception or memory—a type of memory illusion, although there is no single, agreed-upon model that explains exactly what's happening in the brain during an episode.

Déjà vu is sometimes likened not to a "glitch in the matrix", but a small "glitch" in the brain. This occurs when two streams of thought collide, causing a miscommunication between the parts of the brain that play a role in memory recollection and familiarity. The frontal parts of the brain signal that a past experience is repeating itself, while the decision-making areas of the brain fact-check to see whether or not this is consistent with what is possible. If it is possible, the person may try harder to retrieve memories associated with the person or place. If it's not possible, a déjà vu realization can occur. Often, the moment of déjà vu is mundane, like my personal experience above. Déjà vu is commonly associated with fatigue and stress. People who are busy, tired, and anxious often report episodes of déjà vu.

There are also medical causes for déjà vu. People with temporal lobe epilepsy, schizophrenia, vascular dementia, and related psychiatric or neurological conditions might experience déjà vu and vivid 'memories' more frequently. In rare cases of déjà vécu’, French for "already lived", sufferers have recurring feelings that they've lived previously. Novel situations are experienced as strangely familiar, often leading to a conviction that memories are being recollected from a previous life.

Should we be concerned when we experience déjà vu?

Experiencing déjà vu can catch some people off guard. The eerie experience can make others feel uncomfortable or even fearful that something is wrong. In some cases, déjà vu can be a sign of an underlying neurological or psychiatric issue. But, in general, the experience of déjà vu is nothing to worry about, it's just a matter of memory or perception. In fact, it's a sign that the fact-checking regions of the brain are working well to prevent us from misremembering events.