The sensation of experiencing something and, simultaneously, having a strong conviction that such an event has occurred before is called déjà vu. This expression, which means 'already seen' in French, was introduced in the 18th century by parapsychologist Émile Boirac to characterize this intriguing phenomenon.
Despite being a very common experience, science does not yet have a complete understanding of déjà vu, although it is known that it is not of a paranormal nature. Throughout history, various approaches have attempted to elucidate this mystery, from discussions in Ancient Greece to varied interpretations.
For the field of parapsychology, déjà vu can be interpreted as a form of premonition, while spiritualists link it to out-of-body experiences during sleep. Sigmund Freud also sought to unravel the enigma, associating the phenomenon with unconscious desires or past fantasies. However, the scientific perspective firmly points to an entirely biological origin.
Scientists agree that the cause of déjà vu lies in an error in information transmission within the brain. The human nervous system is continuously comparing new data with scenarios it can predict. One example of this is when the brain, upon observing two high-speed vehicles, anticipates a possible accident.
These two signals—that of current perception and that of prediction—reach the hippocampus, the brain region responsible for making this comparison, almost simultaneously. Déjà vu occurs when there is a desynchronization between these two stimuli upon reaching the hippocampus. If, due to some modification in neuronal activity, the prediction arrives slightly before the perception of the present moment, the brain begins to interpret what is happening as something that has already been experienced.
This lack of synchronization generates the false impression that the current situation is part of our history. In this brief lapse, the individual may perceive a complete scene, including sounds and smells, and feel absolutely certain of having gone through it before, even believing they can 'anticipate' subsequent details. However, it is a temporary illusion, lasting only a few seconds, until the brain can restore its usual synchronization.
