The researchers completed two memory experiments  In experiment 1, participants learned 40 groups of words  In experiment 2, participants learned a series of finger signals  In both experiments, only half of the participants were told that they would be tested in 10 hours  Only some participants were arranged to take a nap between study and test  The results showed that the participants in the sleep group performed better than those who did not sleep, and those who were told in advance to take the test also had higher test scores
Some of the participants who were told to take the test did not fall asleep during the nap, and they unconsciously reviewed what they had learned in their brains
 As a result, researchers believe that sleep helps the brain store memory information that is useful for the future