Who Needs Sleep?

      There are twenty-four hours in a day. This is a fact of which every human - and especially every college student - is well aware. Unfortunately, it never seems as though twenty-four hours is completely enough for everything that needs to get done. It does not help that approximately (allegedly) eight of these hours are dedicated to being completely unconscious. Sleep is such an essential part of the human routine that many of our non-daylight hours are devoted to it. And yet, while we understand the rejuvenated feeling of a good night's sleep or the tired crabbiness of a pre-coffee early morning, no one seems to understand the actual purpose of sleep itself. Studies have shown that people who do not get adequate amounts of sleep are more irritable, have impaired memory, and can even show signs of dementia, but no study has been able to solve the mystery of why we need sleep in the first place.      

Perhaps understanding the biological drive for sleep can help unlock some of its obscurity. The body has two ways of regulating sleep pattern: something called sleep/wake homeostasis and the circadian biological clock, more commonly referred to as "circadian rhythm." Sleep/wake homeostasis is all about achieving balance between wakefulness and sleep. When a person stays awake for a certain amount of time, the body will automatically adjust sleep to compensate for that time spent awake. However, we would spend twelve hours sleeping every night if not for the influence of the circadian rhythm, our internal clock. The circadian rhythm is regulated by the Suprachiasmatic Nucleus in the brain. The Suprachiasmatic Nucleus is a group of cells that detects the presence or absence of light. When light reaches the optic nerve, the circadian clock nudges the body into wakefulness by raising body temperature and releasing cortisol. When no light is present, the release of melatonin is induced to promote sleepiness. It is the combination of sleep/wake homeostasis and circadian rhythm that seems to provide the most beneficial sleep.      

The interesting things start happening when we observe the ways the body responds to lack of sleep. We all know too well the symptoms: irritability, impaired judgment, lack of coordination, and of course, fatigue. However, why is it that the night after the infamous "all-nighter," I have been able to perform the miraculous feat of sleeping until five the next afternoon? It's almost as though I?m making up for lost time - because I am. In cases of sleep deprivation, an interesting factor called "sleep debt" comes into play. When the body loses sleep, it stores the amount of lost sleep to be made up at another time. This would suggest that sleep fills a very important role indeed, and one that cannot be subverted in any way. It is different than other bodily functions, such as metabolism. When a person eats less, the body's metabolism will slow to compensate for the reduced food intake with few consequences, provided that the person is still following a nutritious diet. Sleep does not appear to work in this way. One cannot train one's body to function on less sleep; studies have shown that the negative effects of sleep deprivation continue to persist even after repeated patterns.        

All of these things would seem to indicate that sleep is an integral part of normal functioning. A CBS study agrees, placing its importance in the scheme of evolution. While the need to sleep would be a huge vulnerability factor for any animal, there is no species of animal that does not need to sleep. If sleep?s costs were greater than its benefits, it would almost certainly have evolved out unless it was absolutely essential. Lack of sleep causes huge dips in alertness, which is also a dangerous factor in the wild, leaving organisms more vulnerable to attack. And in a seemingly more relevant example, tired people are more likely to be involved in car accidents due to "micro-sleeps," in which the person suffers a momentary lapse in consciousness while alert.        

So despite the enormous importance of sleep in not just our lives, but the lives of animals, no one seems to know exactly what it is that makes sleep so important. We know the adverse effects sleep deprivation can have, we know the ways in which we are biologically rigged for sleep, and we even know how much sleep we need quantitatively and qualitatively to function. The Centers for Disease Control and Prevention have a page dedicated to "Sleep and Sleep Disorders: A Public Health Challenge," because getting adequate amounts of sleep can help prevent major health issues such as diabetes, cardiovascular disease, obesity and depression. What is it about sleep that plays such an instrumental role in generally keeping us alive?        

Circadian rhythm would seem to suggest that sleep has simply been a way for us to stay out of the way when we were less able to see, in an evolutionary sense. When the light left, we might just find a corner and stay unconscious until the light returned. But the additional presence of sleep/wake homeostasis would suggest that there is something about wakefulness that actually mandates sleep. We find that not sleeping leads to personality changes and disease. It seems that the parts of ourselves that we use throughout the day become depleted, and that sleep is a way for us to restore that depletion. Our immune system, complex brain processes like decision-making, calculation, and even physical coordination, and our digestive system are examples of some bodily functions that run without ceasing while we are awake. Sleep, it seems, provides a way for the body to shut down some of these processes while still allowing very basic functions like the operations of the lungs and the heart, to allow the restoration of the used resources. By not sleeping enough, we are unable to fully restore those resources, which would explain some of the impairments observed by the sleep experiments, and would continue to use these resources as they quickly drain away. This could conceivably lead to death, as was seen in an experiment where rats died after being kept awake for five days. Sleep's importance almost certainly goes deeper, seeing how pervasive the need for sleep is in life itself, but after all, these are simply the musings of a sleep-deprived college student.  Resources: 1. http://www.sleepfoundation.org/article/sleep-topics/sleep-drive-and-your-body-clock 2. http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm 3. http://www.cbsnews.com/stories/2008/03/14/60minutes/main3939721.shtml?tag=contentMain;contentBody 4. http://www.cdc.gov/sleep/