睡眠之谜

介绍：　　NOVA: Mysteries of Sleep Like virtually every other animal, humans need sleep to survive. But why? What do we gain from spending nearly a third of our lives in such a defenseless state? And what's at stake if we sleep poorly? The functions of sleep have long been something of a mystery. But now scientists are peering deep into the brain to see what happens while we snooze. One study reveals that well-timed bursts of pink noise can nudge a person's brain waves, extending periods of slow-w