It’s a phenomenon experienced by mostly every human being on the planet. The feeling that everything you are currently experiencing has happened before but there is no prior recollection of said experience. Déjà vu is a disturbance (delay) in the brain’s “time labelling” mechanism. For an animal to survive in its external environment two of the things it must be able to do are; identify an event and then determine when this event happened in accordance to other events. Take a ship’s log for instance, if you wanted to piece together a ship’s entire history you would find every major event that has occurred and the time it happened within the log (Efron, 1963). The brain is similar to this in that it logs and labels events.
How does déjà vu occur?
When events are perceived the information is relayed to the two hemispheres within the brain, the non-dominant and dominant hemispheres. Usually information is first received by the non-dominant hemisphere and then passed to the dominant hemisphere within a matter of milliseconds. Déjà vu occurs when there is a delay of this information pass over. So essentially both hemispheres perceive the same event but the information pass over is delayed between the two hemispheres. This delay gives the sensation that you have logged the event but the event has never been labelled (Efron, 1963).