Deja Vu
One of the most peculiar tricks that memory can play, Deja Vu is curious, marked by a sudden, intense impression of familiarity – a feeling of ‘being here before’ or having lived through the moment already.
A sense of deja vu can occur in any situation. You may be visiting some entirely unfamiliar town and suddenly feel that you have been right there, in that precise spot, at some other time – even though you know that is impossible. Or you may be talking to friends around the dinner table and feel that you have had this conversation and lived’ this moment before. The feeling goes way beyond any vague sense of having seen or done something similar in the past – it is very precise and unmistakable. Deja vu can seem more ‘real’ than a normal recollection, yet it is maddeningly elusive because, unlike flashbacks or ‘Proustian’ memories, it cannot be pinned down to a past event. Usually, the feeling evaporates quickly and cannot be recaptured; however hard you scour” your memory.
Ideas and explanations
The sensation of deja vu is so singular that some have regarded it as evidence of reincarnation. Another superstitious explanation is that deja vu is the memory of a dream in which the person ‘lived through’ the moment in advance of it happening.
Other more rational explanations have been suggested over the centuries. For example, Freud held that deja vu occurs when a repressed fantasy of doing or seeing something floats p to consciousness momentarily but then returns to the unconscious before it is clearly acknowledged.
One speculative explanation for deja vu is that it may occur as a result of the left and right hemispheres of the brain being slightly out of synchronization. The slight delay in communication causes the two hemispheres to function momentarily as two separate consciousnesses. This may explain why deja vu is sometimes associated with epilepsy and the aura (forewarning) that precedes migraine.
The latest theory
Current brain research suggests that deja vu may be the result of a momentary error in the way the brain constructs conscious perception. Everything we experience is processed along many parallel pathways in the brain. Some of these run through areas of the brain’s outer layer or cortex and deal with sensory perception. For example, they combine visual information to form complete images and link sensory information to related facts, such as the names of objects and what they are. Other pathways run through the limbic system, the brain’s emotional center, and it is here that information is clothed with emotional significance, including, if appropriate, the feeling of familiarity. Normally, the information from the limbic and cortical pathways is brought into consciousness at the same time, creating a ‘full’ picture. Deja vu is thought to occur when information flowing through the limbic system is tagged with familiarity by mistake. When this incorrectly identified information merges with the information from the rest of the brain, it produces a feeling of familiarity that is at odds with the knowledge produced by the cortex. This leads to the puzzling experience of deja vu.
Jamais Vu
Jamais Vu is the converse of deja vu: instead of something new feeling familiar, something known feels strange. You might, for example, be in your own home when suddenly the furniture and the layout strike you momentarily as utterly unfamiliar. Or you may look at someone you know well and feel fleeting that he or she is as strange to you as a face in a crowd. Yet intellectually, you know that the room or the person is exactly as they have always been.
Like deja vu, jamais vu is probably caused by a momentary failure of the limbic system to react appropriately- in this case, information that should be recognized as having emotional significance is not, or the emotional ‘labeling’ does not get through to consciousness.
Although the phenomenon usually lasts for just a few seconds, in rare cases, damage to the limbic pathway can produce permanent jamais vu, especially in regard to people. These feelings may become so intense that the sufferer concludes that friends and family have been ‘replaced’ by impostors or aliens. This conviction, known as Capgras delusion, can have catastrophic consequences. Sufferers often reject their families and may become paranoid and violent.
