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Why do we spend one-third of our lives asleep

This is Science Today. About one-third of our lives is spent sleeping and while it may seem obvious that we need to sleep, scientists don't yet know why.

Walker:          There is no consensus yet amongst the scientific community and in this day and age of amazing molecular biology, stem cell production, all of these amazing technologies, yet still have cracked the question of functions of sleep. And so, that's what we really try and do in the lab.

Narrator:        Matthew Walker directs the Sleep and Neuroimaging Laboratory at the University of California, Berkeley and has found that sleep does far more than refresh the body and mind. It's directly linked to our immune systems, memory and learning, emotional functioning and metabolic control.

Walker:          We achieve many different things when we're awake — both for our brain and our body. And so, why would that same logic not hold true for the one-third of our life that we spend asleep and I think now what we need to try and understand is what are the functions of sleep, rather than just the sole function of sleep.

Narrator:        For Science Today, I'm Larissa Branin.