Neuroscientist Susumu Tonegawa at the Massachusetts Institute of Technology (MIT) has reported on a mechanism for déjà vu (French for “already seen”). We’ve all experienced it, that feeling that you’ve been somewhere, or seen something before, even though you haven’t.
The basis for this feeling, according to Tonegawa, is that you are really experiencing something very similar to something you’ve experienced before, but your brain can’t tell the difference. The part of your brain that helps you distinguish between two very similar experiences is the dentate gyrus. Tonegawa bred some mice in which the dentate gyrus doesn’t function very well and these mice were less able to distinguish between two similar situations than control mice.
As we age, the dentate gyrus becomes less functional, which explains why déjà vu happens more frequently as we get older.