Noted: Researchers are growing increasingly confident, though, that sleep evolved specifically to recharge the brain. Dr. Chiara Cirelli, a neuroscientist at the University of Wisconsin, has been studying the difference between sleep and quiet wake in humans. She says that while we?re awake, all of our neurons are constantly firing, but that when we?re asleep, the neurons revert to an “up-and-down” state in which only some are active at a given time. During some stages of sleep, all neuron activity goes silent. And that?s likely when the restful part of sleep takes place.
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