National Geographic : 2010 May
doesn't serve an absolutely vital function," the renowned sleep researcher Allan Rechtscha en once said, "it is the greatest mistake evolution ever made." e predominant theory of sleep is that the brain demands it. is idea derives in part from common sense---whose head doesn't feel clearer after a good night's sleep? But the trick is to con rm this assumption with real data. How does sleeping help the brain? e answer may depend on what kind of sleep you are talking about. Recently, researchers at Harvard led by Robert Stickgold tested undergraduates on vari- ous aptitude tests, allowed them to nap, then tested them again. ey found that those who had engaged in REM sleep subsequently per- formed better in pattern recognition tasks, such as grammar, while those who slept deeply were better at memorization. Other researchers have found that the sleeping brain appears to repeat a pattern of neuron ring that occurred while the subject was recently awake, as if in sleep the brain were trying to commit to long-term memory what it had learned that day. Such studies suggest that memory consolida- tion may be one function of sleep. Giulio Tononi, a noted sleep researcher at the University of Wisconsin, Madison, published an interesting twist on this theory a few years ago: His study showed that the sleeping brain seems to weed out redundant or unnecessary synapses or con- nections. So the purpose of sleep may be to help us remember what's important, by letting us forget what's not. Sleep is likely to have physiological purposes too: at patients with FFI never live long is likely signi cant. A lot of interest has focused on what exactly kills them, but we still don't know. Do they literally die from lack of sleep? And if not, to what extent does sleeplessness contribute e genetic history of sisters Carolyn Schear (at right) and Cheryl Dinges puts them at risk for fatal familial insomnia, a deadly inability to sleep. Schear learned she doesn't carry the gene. Dinges declined testing. "Why let the knowledge rule your life?"