Researchers measured heart and electrical activity of the brain during sleep. They found that the beat-to-beat variation in heart rate accounted for much of the previously unexplained variation in how well people performed on memory and creativity tests following a nap.

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Researchers measured heart and electrical activity of the brain during sleep. They found that the beat-to-beat variation in heart rate accounted for much of the previously unexplained variation in how well people performed on memory and creativity tests following a nap.