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At the start of the 21st century, scientists had little idea why we sleep, leading J. Allan Hobson at Harvard Medical School to quip that the only known function of sleep was to cure sleepiness. But 20 years later, we know a lot more. It turns out that for every two hours a person is awake and interacting with the world, the brain on average needs to go “offline” for an hour—disconnected from the outside world—to process and contextualize those experiences.
Sleep benefits memory in myriad ways. For simple procedural skills—how to ride a bicycle or distinguish between different coins in one’s pocket—a night of sleep or an afternoon nap following learning leads to a dramatic improvement in performance. Sleep also stabilizes verbal memories, reducing their susceptibility to interference and decay, processes that all too easily lead to forgetting.
But the action of sleep can be ...
