Light and deep NREM sleep and REM sleep “offer different brain benefits at different times of night” (108). One of the primary advantages conferred by sleep, especially NREM sleep, is aiding the brain in solidification of fact-based memories. During NREM sleep, memories stored in the hippocampus, which serves as the short-term storage area for memories accumulated during the day, transfer to the cortex, or the “long-term secure vault” (111). This nightly process restores the brain’s capacity for learning and making new memories because it prevents the hippocampus from exceeding its storage capacity. Sleep spindles aid this process and are particularly rich in the late-morning hours. Moreover, individuals can better recall information they learned if they have greater amounts of deep NREM sleep. The brain does not save all memories. It deletes information not needed, which makes memory recollection easier and more efficient. Sleep spindles play a key role in selecting which memories to save.

NREM sleep also helps the brain to improve skill/motor memories. Walker’s own research demonstrates that practice of the skill, such as sequencing a set of numbers on a keyboard with an individual’s non-dominant hand, followed by a night of good, natural sleep results in individuals perfecting the skill.