The following is an excerpt from James McGaugh’s Book Memory & Emotion:
Robert Stickgold and his colleagues reported that human subjects improvement on a visual discrimination task occurred only after the subjects had had a night’s sleep and that, most interestingly, the improvement varied directly with the amount of slow-wave sleep during the early hours of sleeping and with the amount of REM sleep occurring in the few hours before waking. These findings strongly supposed Heine’s hypothesis that processes occurring during sleep, and not the passage of time, are responsible for the consolidation of the memory of the visual discrimination training. They also found that, with no additional training, further improvement in performance occurs after a second night’s sleep; but that improvement requires the first night’s sleep. Sleep also promotes the consolidation of motor skills. Jan Born and his colleagues found that eight hours of sleep following practice on a finger-tapping motor skill greatly improved subsequent performance on the task. These findings may well have important practical implications. Born and his colleagues suggest: “In generalizing these observations to skills of everyday life (such as learning a musical instrument or sport) we would conclude that sleep is required to achieved optimum performance on any of these skills.” The fact that my high-school and college band and orchestra rehearsals were typically scheduled early in the morning of the school day may help explain (one reason among a great many) why it is that I didn’t not become a professional musician. However, in developing such a skill it is clear that, although sleep may be necessary, it is clearly not sufficient!
The findings of these animal and human studies are clear and consistent: sleep promotes memory consolidation.