Friday, April 20, 2012

Déjà Vu

Déjà vu is a French expression meaning "already seen," coined by French parapsychologist ÉmileBoirac in 1876 to describe an inexplicable – and often unsettling – sensation of familiarity while experiencing something for the first time. Although déjà vu has become a blanket term for any experience of this feeling, it technically only applies to visual information. Later researchers further divided this sensation into déjà visite ("already visited"), déjà vecu ("already lived through"), déjà senit (“already felt”), and déjà entendu ("already heard").

Though some parapsychologists suggest psychic sensitivity or resurfaced memories from past lives, conventional science offers its own explanations. Some researchers credit déjà vu to cryptomneisa – forgotten memories that resurface but register as “new.” Others suspect déjà vu occurs when an experience bypasses perception and goes straight to memory, only to be perceived and remembered simultaneously a moment later.

One school of physiologists link déjà vu to infrequent, minor-level seizures, common to healthy brains; this ripple of electric activity triggers an unwarranted sense of familiarity. The seizure theory is consistent with the increased rate of déjà vu in people with Temporal Lobe Epilepsy (TLE), a chronic neurological disorder characterized by recurrent seizures.

TLE patients may also experience jamais vu (“never seen”) – in effect, the opposite of déjà vu: familiar things seem alien. As a severe example, a schizophrenic individual might encounter a loved one and insist she is an imposter. Though the patient perceives that the “imposter” looks just like the “original,” he experiences a disconnect between this physical data and the expected emotional response from seeing that loved one. Therefore, the patient’s brain rationalizes that this person must be an imposter, because they don’t feel anything towards them.

As a more mundane example of jamais vu, you might doubt that “lozenge” is a real word if asked to say it aloud one hundred times. This repetition results in “mental fatigue”: the brain access the word so repeatedly, it begins to disassociate from its meaning and context, and seems like nonsense.

Finally, presque vu (“almost seen”) describes that “tip of the tongue” (ToT) sensation while trying desperately to recall familiar information. ToT sufferers can often name features of the unrecalled thing, the first letter, and/or similar sounding or similar meaning words. Like déjà vu, ToT occasionally happens to all healthy brains; but when it occurs frequently, it can indicate dysnomia learning disorders or asnomia from brain injury.

Although presque vu’s causes are not well known, the blocking hypothesis posits that the target word is inhibited by thinking of “almost guesses” – things like or related to the target. So the “helpful” person throwing out not-quite-right suggestions might actually be preventing access to what you hope to recall. This is why one will usually recall the target word after they stop trying to remember it.

Although these anomalies can be eerie or annoying, they actually help neuroscientists unravel the mysteries of memories. So the next you’re disturbed by déjà vu or plagued with presque vu, keep calm and remember this post.

Source: 1, 2, 3, 4, 5, 6