If you've ever had that fleeting, mysterious sense that something new -- a city or person you’re seeing for the first time -- is somehow familiar, that you’ve been there or known them before, then you can count yourself among those who have experienced déjà vu. It’s typically a brief sensation, lasting no more than 10 to 30 seconds, but 96 percent of the population claims to have experienced at least one occurrence. source

Obviously, many people worldwide think the deja vu is real and claim to have experienced it, but has it ever been proven to exist under proper observing conditions?

If so, is there a scientific (physiological, neurological, psychological etc) explanation for the phenomenon?