(x-post from my old blog)
Deja vu, the phenomenon of feeling that events occuring have occured
before in exactly the same fashion, can be explained very simply as a
matter of timing in the brain's processing of events. It's not hard to
imagine that some aspects of a stimulus are processed faster than
others. Have you ever raised your head before you "heard" the telephone
ring--before your frontal lobes perceived and recognized a sound?
Hearing a sudden, unexpected noise will cause an almost reflexive
reaction in most humans. They jump and look towards the origin of the
sound. It isn't necessary to fully perceive sounds like that prior to
responding to them, and because such noises could signal danger, it
could be a deadly mistake to rely on the much slower frontal lobes to
finish up before a response is coordinated.
A similar system is
likely in play during deja vu. A stimulus is perceived and processing
begins on it. However, the memory storage process encodes the stimulus
just a fraction of a second before the frontal lobes. The frontal lobes,
in processing the stimulus, refer to memory, including the memory just
encoded for the same stimulus, and therefore recognize the stimulus as
something _that already happened_. This out-of-step-processing
hypothesis also explains the decay of deja vu. As an episode of deja vu
progresses, the two processes of conscious perception and memory
gradually return to their proper order, closing the time gap until
conscious processing overtakes memory processing. This closing gap
agrees with the experience of the deja vu memory becoming progressively
less certain until events no longer appear to have happened before.
It's
still not clear what causes deja vu or why episodes tend to stick out
in a person's memory. Memories are more concrete when the stimulus is
very strong or traumatic to the observer, but that doesn't imply that
the processing is *faster*, and furthermore the events that surround
episodes of deja vu are typically very mundane and in no way emotionally
charged. Possibly, deja vu merely shows evidence of the brain's
imperfect powers of perception and time gaps result from a race
condition in our brain software. The more common explanation, that deja
vu arises from the association of long passed or familiar memory traces
with present stimuli could provide part of the answer. Assuming that the
memory process must precede the conscious proces we have to assume that
either the conscious process slows or the memory process accelerates
prior to an episode. If the prior-memory-association hypothesis is
correct, then it's possible the memory of a past event is substituted
into evolving memory and thereby speeds up the process.
My
hypothesis comes from a conceptualization of the brain as a sort of
neurochemical computer. I assume that certain processes are distinct,
identifiable, and observable. I may be wrong and the brain may be
organized in ways that I did not anticipate and cannot understand. Even
so, my explanation is at least as good as any other I've heard and I
beleive it can be tested with in a drug trial.
