The What and Why of Sleep 

Here are some preliminary answers—though research on the benefits of sleep for humans is still underway and we are likely to know more in another year or two than we do now. Before focusing on these benefits, we would like to set the stage by describing something about the unique way in which our brain lets us know that sleep offers such important benefits. Our brain, in fact, is willing to short-circuit all other functions of our body to demand that we fall asleep.


The Brain’s Demands

Only the brain needs sleep. Other parts of our body are not in need of anything quite similar. It is interesting that we use the same word, “tired”, when describing the conditions leading to both sleep and cessation of physical activity. We spend an hour working in the garden or completing a run of 5 miles – and we are “tired”. Our body suggests that we take a little time off from physical labor and rest a bit. However, it is only a suggestion being made by our body. We can ignore the suggestion and continue to garden or run another five miles. Sometimes (at least in the logo of sports psychology) we “will” our body into doing a bit more work – and we ignore (at least temporarily) the signals emanating from our body regarding the value of reduced physical activity.

Such is not the case when we speak about being “tired” and needing to get some sleep. Our brain is not offering a suggestion. Rather, it is commanding that we fall asleep. It is very hard to ignore this command. We will tend to fall asleep – even if we are driving a car or trying to watch a movie. The demand for sleep can lead to the inconvenience of a missed movie or to the much more serious consequences of an automobile crash and the potential loss of lives. The chemicals involved in this demand for sleep are quite powerful and tend to override other chemicals that help to keep us awake.

It is also the case that when these chemicals are not present, it is very difficult to fall asleep. Our brain is doing a very good job of sustaining our vigilance and consciousness – even though we wish this were not so. We can do a few things to at least temporarily “trick” our mind (and body) into staying awake, whether this be ingesting caffeine or thinking about something that is filled with anxiety (what Robert Sapolsky describes as the human’s ability to imagine attacking lions in the form of financial, work-related, family-related, etc. fears and apprehensions). Neither of these alternatives is very attractive or healthy over the long term. There should be other ways to stay awake – or we should attend to our brain’s demands that we get some sleep.


Why Do We Need Sleep?

The benefits offered by sleep tend to circle around three important perspectives: (1) homeostatic regulation, (2) restoration and repair of bodily functions, and (3) storage and adjustment of mental functions. While these three perspectives are closely related, they do seem to arise from somewhat different sources of concern and interest. If you put together all of their limited perspectives, then you get an accurate sense and picture about the whole, complex biological process called Sleep.

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 memory. Without sleep, the information is worthless, except for the exam grade.

The Damage of Sleep Debt

With these three perspectives in mind, we can turn briefly to the specific impacts that take place if we don’t get enough sleep. The sleep debt accumulates, and, as a result, a lot of bad things can happen. There are many well-established relationships between sleep and physical health, mental health and cognitive functioning. The physical consequences of inadequate sleep and the accumulation of sleep debt include obesity, diabetes, vulnerability to infections, and cancer. The complete list is much, much longer. We can also point to the accidents and performance decline that comes with lack of sleep.  Remember falling asleep at the wheel?

When we turn to the consequences in terms of mental health, we can identify a list that is just as disturbing. First and foremost is the relationship between sleep debt and depression. There are many reasons to believe that the increase of depression in the United States is related to a reduction in the amount and quality of sleep among our citizens. Sleep debt also relates to our ability to manage anxiety, control our rage and remain emotionally stable and “emotionally intelligent” when relating to other people. Perhaps of greatest importance is the strong relationship between sleep debt and suicide attempts (and tragically successes). The bottom line: we can die from sleep debt.