"We don't sleep just to rest our tired bodies?" Stahl asks Matthew Walker, the director of the Sleep and Neuroimaging Lab at the University of California, Berkeley.
"Well, that's been one of the long-standing theories. But I think what we're starting to understand is that sleep serves a whole constellation of functions, plural," Walker explains.
One thing that's clear, says Walker, is that sleep is critical. In a series of studies done back in the 1980s, rats were kept awake indefinitely. After just five days, they started dying.