Why It is Important to Sleep: Repair and Restore, Mental Alertness, and The Evolutionary Theory

Sleep, we all need to do it but why? This question has been pondered by layperson and scientist alike throughout time. Whereas before there were only philosophical theories to go by today, modern scientists have come a bit closer to the truth because of technology and the invention of the electroencephalograph and other devises which actually record our brainwaves during the sleep process. This great machine led to the discovery of the sleep cycles that all humans pass through.

This brings us back to the question, why do we need to sleep?

There are several theories but the most known theory is the theory that the body uses this time to repair and rejuvenate itself, otherwise as organisms, we would just breakdown from fatigue and exhaustion. Anyone who has spent sleepless nights would adhere to that. They will note that they are not only physically fatigued but mentally fatigued as well.

Repair and rejuvenate sleep theory

This theory purports that it is the four stages of non-REM sleep that repairs and rejuvenates the body in preparation for the next day. The non-REM stages are the stages that are dream free. Whereas the REM stage, the rapid eye movement stage, is the dream stage and it is this stage that is vitally important for our mental health. Our mental processes such as our cognitive functions, our ability to think, learn and understand the environment around us is repaired and revitalized when we go into REM sleep.

Scientists have discovered that when people are sleep deprived, once allowed to sleep, they will have longer than normal REM sleep, clearly showing the importance of REM sleep, (dreaming) for restoring our body's equilibrium. Longer REM sleep will also happen after physical activity as well.

During all 5 sleep stages, the body is restoring itself in one way or another. Psychologists have discovered that during sleep, the level of cell division and protein synthesis increases, adding even more credence to this theory of reparation.

Adaptive theory for sleep

The adaptive theory for sleep is also known as the evolutionary theory. This sleep theory maintains that sleep is for the purpose of conserving energy and is seen in all animal species. The theory maintains that we sleep when it is most adaptive for us to sleep. For example, humans normally sleep at night because in our early days of evolution wild animals were on the prowl at night, and it was beneficial for us to be secluded away from the danger of the night. Also, we needed to the sun to hunt and gather and to feed ourselves. Therefore sleeping at night was the most logical thing to do.

We have also discussed in a previous article, how our circadian rhythms are very sensitive to light and dark. When it is dark, the body produces a hormone called melatonin which causes us to become drowsy and prepares us for sleep.

The evolutionary or adaptive theory holds true for animals as well. Large animals such as lions that can pretty much defend themselves in the open, sleep up to 15 hours at a time. On the contrary, small animals that are prey for other animals cannot afford the luxury of sleeping as much. They must always be vigilante and therefore they sleep only about 5 hours at a time. Sleeping for them is the time they are most vulnerable.

Therefore according to the adaptive or evolutionary sleep theory, sleep is a necessary relaxation from a period of great activity and it is also adapted to the environment in which we live. 

Information Consolidation Sleep Theory

The Information Consolidation Sleep Theory is the sleep theory purported by cognitive psychologists. This theory says that sleep is important to process the information that we receive during the normal course of the day. It also suggests that sleep helps us to internalize what has happened during the day so that it will enter and stay in our long term memory. It further purports that sleep may actually prepare us mentally to absorb the new information and be able learn (especially important for students) the following day.

Support for this theory is clearly shown in sleep deprivation research. People who do not get enough sleep are irritable, jumpy, have poor concentration, and do not process information as quickly as they should. Sleep deprivation not only results in students with poor grades, it impacts on our entire life; from straining family relationships, to bad performance on the job, to traffic accidents and so on.

More to be said on sleep deprivation and insomnia to follow.

More likely than not sleep is not confined to any one of the theories. Each of these theories explain just a certain part of the importance of sleep.

Sources:

http://psychology.about.com/od/statesofconsciousness/p/TheoriesofSleep.htm