Sleep is not the absence of wakefulness. It is far more than that.

Described earlier, our nighttime sleep is an exquisitely complex, metabolically active, and deliberately ordered series of unique stages.

Numerous functions of the brain are restored by, and depend upon, sleep. No one type of sleep accomplishes all. Each stage of sleep—light NREM sleep, deep NREM sleep, and REM sleep—offer different brain benefits at different times of night. Thus, no one type of sleep is more essential than another. Losing out on any one of these types of sleep will cause brain impairment.

Up to this point, we have discussed the power of sleep after learning to enhance remembering and avoid forgetting. However, the capacity to forget can, in certain contexts, be as important as the need for remembering, both in day-to-day life (e.g., forgetting last week’s parking spot in preference for today’s) and clinically (e.g., in excising painful, disabling memories, or in extinguishing craving in addiction disorders).

Moreover, forgetting is not just beneficial to delete stored information we no longer need. It also lowers the brain resources required for retrieving those memories we want to retain, similar to the ease of finding important documents on a neatly organized, clutter-free desk. In this way, sleep helps you retain everything you need and nothing that you don’t, improving the ease of memory recollection. Said another way, forgetting is the price we pay for remembering.