NOVA: The mystery of sleep is like almost all other animals, humans need sleep to survive. But why? What can we gain by spending nearly one-third of our lives in such a defenseless state? What are the dangers if we don't sleep well? The function of sleep has always been a mystery. But now, scientists are delving deep into the brain to observe what happens when we take a nap. A study has shown that timely bursts of pink noise can drive a person's brain waves, prolonging the duration of slow waves or deep sleep. Toddlers who learn new words have shown that even taking a nap after learning a new word can help them remember information. When it comes to sleep deprivation, it may be found that sleep interruption is as harmful as completely missing sleep. As scientists gradually understand the powerful role that sleep - or sleep deprivation - plays in everything from memory to trauma to emotional regulation, one thing is clear: this biological function is both complex and crucial.