Narrator: This is Science Today. There have been many theories about the exact function of sleep - some ideas dating back to the ancient Greeks. Neuroscientist Marcos Frank of the University of California, San Francisco, says there are currently about half a dozen theories - ranging from those having to do with learning and memory to ideas that sleep may be a time to detoxify noxious substances that accumulate during waking hours.
Frank: But the evidence for any one of these theories has been scant over the years, although at least recently there's been an accumulation of evidence that tends to lend more credence to the idea that sleep is important for learning and memory. And that's kind of where our study comes in.
Narrator: Their study on sleeping cats demonstrated the first clear evidence that sleep provides a time for significant brain growth - or plasticity - after a period of stimulation or learning.
Frank: Now that we've demonstrated that sleep matters, now we want to know why. So the next questions are really to deal with mechanism. So that's the next real step is to figure out what exactly sleep is doing.
Narrator: For Science Today, I'm Larissa Branin.