Why does déjà vu happen, and can science explain it?

You’re walking into a place you’ve never been to before. And yet, for a fleeting moment, it feels known. Not vaguely familiar, but specific, like a memory you can’t fully access.

Strange as it sounds, this experience is real, common, and studied. It is called déjà vu.

What is déjà vu?

Déjà vu, a French term meaning “already seen”, refers to a moment when a new situation feels familiar. Studies suggest that nearly two-thirds of people experience it at least once in their lives.

Akira O’Connor, a senior lecturer in the School of Psychology and Neuroscience at the University of St Andrews, explained this clearly while speaking to BBC:

“In scientific terms it’s an inappropriate sense of familiarity for something that we know to be unfamiliar.”

In simple terms, your brain signals that something has happened before — even when you know it has not.

When did people start studying it?

People have written about déjà vu for centuries. But it became a subject of study only in the 19th century.

The term is often linked to Émile Boirac, who used it in the 1870s in his work The Psychology of the Future. Early explanations ranged from supernatural ideas to basic sensory errors.

One theory suggested that déjà vu happens when signals from the eyes or brain reach at slightly different times. This creates a delay that the brain reads as a repeated experience.

The causes of déjà vu

Scientists today look at déjà vu through brain function, not mystery. According to Dr O’Connor, the explanation lies in how different parts of the brain interact.

One key area is the medial temporal lobe. This part helps store memories and creates the feeling that something is familiar. Another important area is the frontal cortex, located in the front of the brain, which checks facts and helps with decision-making.

Dr O’Connor said, “there’s a part of the brain in the medial temporal lobe, associated with laying down memories and giving you the feeling of remembering things.”

Here is how the process is understood:

• The medial temporal lobe mistakenly triggers a sense of familiarity
• The brain signals that the current moment has happened before
• The frontal cortex checks this signal
• It identifies the mismatch and labels it as an error

This entire sequence happens quickly, which is why déjà vu lasts only a few seconds.

Why does it happen more at certain ages?

Research shows that age plays a role.

Dr O’Connor said that people begin experiencing déjà vu around the age of five. The frequency increases during teenage years and peaks in the early to mid-20s. After that, it becomes less common.

This pattern may be linked to how active memory systems are at different stages of life.

Is déjà vu a problem?

Many people think déjà vu is a memory issue. But research suggests otherwise. Dr O’Connor explained: “On the whole, I would say it's a sign of a good, healthy brain and mind.”

The experience shows that the brain’s checking system is active. It detects an error and corrects it.

A related phenomenon: ‘Jamais vu’

Déjà vu is not the only memory-related experience.

There is also jamais vu, which means “never seen”. It is the opposite of déjà vu. In this case, something familiar suddenly feels unfamiliar.

Dr O’Connor and his colleagues studied this effect and were awarded the Ig Nobel Prize for Literature in 2023. Their work showed that repetition can trigger this feeling.

For example, when you write or read a common word many times, it may start to look incorrect or unfamiliar.

“People were most likely to experience the sensation of unfamiliarity for the most frequently used words, so words like ‘the’,” Dr O’Connor said.

So, can science explain déjà vu?

Science does not have a single, final answer. But current research gives it a clear direction.

Déjà vu is not a mystery event or a sign of something unusual. It is a short mismatch between memory and awareness. The brain generates a false signal of familiarity, then corrects it.

What feels strange in the moment is, in fact, part of a normal process. And the next time it happens, it may not feel any less unusual — but you will know where it comes from.

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