Quote Originally Posted by Gandalf_The_Grey
Deja Vu is caused by one side the brain processing information with a slight delay, being a split second behind the other side of the brain. This makes you think you've seen this all before because, as far as mental processing goes, you are seeing it a second time around; just within a micro-second.

It's also natural for the mind to super-impose this seemingly repeating information on past memories, to make sense of the double info processing.
Your brain does not delay processing information by a split second. That is the biggest load of shit I have ever heard. Every neuron fires about 200 times every second and I highly doubt that it would delay for a "split second" when it's that fast.

This kind of makes sense, it doesn't give an answer but it gives you things to consider: HowStuffWorks "How Deja Vu Works"