First, the homeostatic perspective. This is the most general perspective – and it relates directly to the demands being made by the brain. Our entire body is devoted on an ongoing basis to remain in some balanced state. We don’t want to be too warm or too cold and we don’t want to be too active or too sedentary. Most importantly, we want to balance off the time we are alert and active with the time we are inactive and restorative. There is a rhythm to our daily life (that we will describe shortly) and this rhythm results in a cycle requiring a period of sleep. If we don’t get enough sleep, then there is a sleep debt that accumulates—requiring that we fall asleep. This is the demand being made by our brain.
This first perspective is valuable in that it provides us with a compelling image of the demand for sleep—but it still doesn’t tell us why we need this cycle. The second perspective provides at least part of the answer. The brain needs the sleep because it is working on behalf of the welfare of other parts of our body. Every part of our body requires long periods of sleep—in order to restore and rejuvenate as well as develop. Our body needs time off from being active in order to grow muscle, repair tissue, and synthesize hormones. As we noted about, if the body can’t demand that we rest when we are tired, then the brain can make the demand and produce the required rest provided by sleep.
This second perspective is very helpful, but it still isn’t enough, for the brain is not just a self-less protector of our body’s welfare – it also has its own specific reasons for demanding sleep. Let us turn to the words offered by Matthew Walker (2017, p. 7) in his highly informative book, Why We Sleep:
Within in the brain, sleep enriches a diversity of functions, including our ability to learn, memorize, and make logical decisions and choices. Benevolently servicing our psychological health, sleep recalibrates our emotional brain circuits, allowing us to navigate next-day social and psychological challenges with cool-headed composure.
To offer one specific example of the critical role played by sleep in this functioning of the brain, researchers have recently begun to examine ways in which we reorganize our memory system during sleep. Information we have collected during the day, that are stored in a short-term memory system, are sorted, coded and selectively retained during sleep and moved to a long-term memory system. This is part of the reason why students can stay up all night to study for an exam held the next day and can pass this exam with flying colors – yet remember nothing the following day. They were able to use the information contained in short-term memory for the exam, but none of this information was transformed and placed in long-term member. Without sleep, the information is worthless, except for the exam grade.
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