Déjà vu – we’ve all experienced it; that weird sensation when an event or experience seems so familiar that you’re sure it has previously occurred, when in fact it hasn’t. A feeling so strange, in fact, that… well, that you can only say what it is in French.
As a rule, humans don’t tend to experience the sensation until the age of 8, though it can occur beforehand. Experiences tend to become more prevalent through childhood and reach a peak in teenage years, and early “tweens” – here, it seems, rates of experiencing déjà vu decrease with a steady growth in maturity. This, obviously, puts forth the argument that déjà vu may be connected to brain development. However:
In his 1928 book A Textbook of Psychology, psychologist Edward B. Tichener suggested déjà vu occurs when we catch a momentary glimpse of a situation, or object, before our brain has fully constructed a conscious, cohesive understanding of the experience, and this “partial perception” leads to a false sense of familiarity. He argued that déjà vu is merely a “false recall” of memory, an anomaly, and not an act of prophecy or precognition, as it was once believed.
When subjects experience a strong recollection of déjà vu, but not specific experiences or circumstances, it is possible this occurs due to a neurological overlap between the systems responsible for short-term memory, and those designed for long-term memory, thus causing recent memories to be perceived has happening further in the past (see the Multi-Store memory storage model). This theory also corresponds with another, which suggests that the brain processes some, and perhaps all, sensory inputs as a “memory-in-progress” – therefore, during the procedure, the brain perceives the event to be a past memory.
A 2004 survey conducted by A.S. Brown, which found two-thirds of the population to experience déjà vu and, thus, the argument for brain development could have its merits – in may indeed be related to the development of memory, the strengthening of neurological separations between our short and long term memories. It must be considered, however, the Brown’s study proves many adults still experience the phenomenon, albeit less often than those in younger age groups – whether this indicates memory is still not a fully developed brain mechanic remains to be seen.
Conclusion (TL;DR) – Déjà vu occurs when our brain crosses wires in memory storage and causes recent memories to appear old.
P.S. A shout out to Stephen King for lending one of his short-story titles to the rather weak joke in my opening paragraph.