What's up with forgetting? You run into your boss in the store and you can't remember her name--it's embarrassing. You're there to buy four items and you can't remember three of them--it's annoying. You're giving a speech and suddenly you can't remember what you were going to say next--it's humiliating. And let's not forget tests: All year you've been studying European history, and suddenly you're drawing a blank--who was Charles the Bald again?

Where are they stored, these memories? How come you can't find one when you need it, but later--when you're playing tennis--there it suddenly is? Of course memories aren't the brain's equivalent of videotapes that you simply haul up from some archive. But then what are they?