Déjà vu, a French term meaning "already seen," describes the uncanny sensation of having previously experienced a current situation, despite knowing it's happening for the first time.1 This phenomenon is characterized by a fleeting sense of familiarity, typically lasting only seconds or minutes, often triggered by sights, sounds, or smells.1 While the exact prevalence is uncertain, studies estimate that 60-70% of people in good health experience déjà vu at least once in their lifetime.2 The feeling is more common among young adults, particularly those aged 15-25, and tends to decrease with age.23 Factors such as frequent travel, regular dream recall, and higher levels of education have been associated with an increased likelihood of experiencing déjà vu.4

Several theories attempt to explain the phenomenon of déjà vu, ranging from memory-related explanations to neurological hypotheses. The split perception theory suggests déjà vu occurs when an initial incomplete perception is followed by a more complete one, creating a false sense of familiarity1. Memory recall theories propose that déjà vu results from the brain incorrectly matching a new experience with a past one, or from forgotten memories being triggered by similar current experiences12. Neurological explanations include minor brain circuit malfunctions, where a brief electrical disruption causes the brain to misinterpret a current event as a memory1. Another theory suggests delayed processing, where information reaches the brain through two separate paths, and a slight delay can make a single event feel like two experiences1. Recent research using virtual reality has also explored the "Gestalt familiarity hypothesis," which proposes that déjà vu may arise from encountering environmental layouts similar to previously experienced but forgotten scenes2.

Scientific investigations into déjà vu face significant challenges due to its spontaneous and fleeting nature. Researchers have employed innovative techniques to study this elusive phenomenon in laboratory settings. One approach, used by the Leeds Memory Group in 2006, involved creating memories under hypnosis and then manipulating participants' ability to recall them, potentially triggering déjà vu experiences1. Another method utilized virtual reality, where researchers created spatially similar scenes in video games to induce déjà vu sensations2. These experimental findings suggest that déjà vu may be a memory phenomenon, occurring when we encounter a situation similar to a past experience that we cannot fully recall2. Interestingly, fMRI studies have shown that déjà vu activates brain areas involved in decision-making rather than memory, leading some researchers to propose that it may be a form of conflict resolution in the brain, checking for discrepancies between perceived and actual experiences2.

Déjà vu experiences exhibit notable age-related patterns, with younger individuals reporting more frequent occurrences. Studies indicate that déjà vu is most common among people aged 15-25 years, with the frequency gradually decreasing as individuals age12. This trend is particularly intriguing as it contradicts the typical pattern of memory issues increasing with age. Researchers suggest that déjà vu may actually be a sign of a healthy mind capable of recognizing incorrect familiarity signals2. While déjà vu is typically harmless, frequent occurrences accompanied by symptoms such as fear, racing heart, or unconscious repetitive motions may be associated with neurological conditions like temporal lobe epilepsy and should be evaluated by a healthcare provider13.