Scientists still can not agree on why we experience déjà vu

Déjà vu — French for "already seen" — is a brief, powerful conviction that the situation you're currently living through has happened before, even though there's no actual memory to back it up.

Most people experience it, most often in young adulthood, and episodes tend to become less frequent with age — which is itself strange, since memory usually gets worse with age, not better.

Competing hypotheses include a brief "glitch" in signal processing between the brain regions responsible for memory and perception, tiny electrical discharges in the temporal lobe resembling microscopic seizures in otherwise healthy people, or an error in the brain's familiarity-recognition system.

None of these theories has been conclusively confirmed as the sole cause — the phenomenon is too brief and unpredictable to study easily under lab conditions, making it one of the more elusive everyday mysteries of the brain.