Neuroscience of déjà vu

Déjà vu all over again

Researchers believe that a set of neurons called place cells fire to provide a sort of blueprint for any new space we encounter. The next time we see the space, those same neurons fire. Thus we know when we've been somewhere before and don't have to relearn our way around familiar turf.

But if we enter a space very similar to one we have seen before, a new but overlapping set of neurons creates the blueprint. When there is enough overlap between the two sets, we experience an eerie feeling of déjà vu--a French phrase that literally means, "already seen."