An hour-long "power nap" can be as beneficial as a whole night's sleep - but only if you dream, a new study suggests.
Scientists who tested the visual learning ability of volunteers found that dozing off for 60 to 90 minutes improved performance as much as sleeping for eight hours. But napping only worked when it included two kinds of sleep - slow-wave sleep (SWS) and rapid eye movement (REM) sleep.
Psychologists at Harvard tested the volunteers' ability to identify the position of bars on a screen. The tests were carried out at 9am, 7pm in the evening, and 9am the next morning.
Volunteers who were not allowed to nap saw their performance decline by the evening of the first day. But those who napped for an hour with both SWS and REM sleep did better than no-nappers at 7pm. But nappers who did not enter REM sleep showed no improvement.
The scientists, writing in Nature Neuroscience, found napping also added to the benefits of a night's sleep. "From the perspective of behavioural improvement, a nap is as good as a night of sleep."
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