We spend about one-third of our lives sleeping, but much of that function remains a mystery. Weekend Edition Sunday is asking some pretty fundamental, yet complicated, questions about why we do it and why we can't seem to get more of it.

Dr. Matthew Walker says the question of why we sleep remains "that archetypal mystery."

Walker, the principal investigator at the sleep lab the University of California, Berkeley, works with patients who suffer from sleep abnormalities. He says the complexity of sleep makes the research that much more fascinating.