What causes deja vu?

The answer

Deja vu, experienced by roughly 60 to 70 percent of people, is now believed to result from a momentary misfire in the brain's familiarity-detection system. The leading neuroscience theory suggests that the medial temporal lobe, which normally assesses whether a current experience matches stored memories, occasionally generates a false familiarity signal for a novel situation. Brain imaging studies in epilepsy patients have shown that deja vu can be triggered by electrical stimulation of the rhinal cortex. A competing theory proposes that deja vu occurs when a scene partially matches a stored memory that cannot be fully recalled, creating a conflict between the feeling of familiarity and the knowledge that the situation is new.