The differing roles of NREM and REM sleep in the slow enhancement of skills and schemas

Sleep's effect on memory may not become evident for several days or weeks after learning, especially for motor skills and schema-related learning. Here, we propose a potential mechanism which may be underlying the slow enhancement of skills and schemas by examining the biological events which take place during NREM and REM sleep. We suggest that the immediate benefits of sleep are mainly due to reactivation during NREM sleep, while the delayed effects are mainly due to plasticity-related changes occurring at the molecular, cellular and system levels, and which require long periods of time to occur. There is increasing evidence that these events may take place preferentially during REM sleep, thus shedding further light on the function of this sleep stage.