1) Repair and Restoration of sleep
This theory postulates that sleep is essential for revitalizing and restoring the physiological processes that maintains the health and function of the mind and body in check. It suggests that NREM (non-rapid eye movement) sleep is important for restoring physiological functions, while REM (rapid eye movement) sleep is essential in restoring mental functions.
During sleep, the body also increases its rate of cell division and protein synthesis, further suggesting that repair and restoration occurs during sleeping periods.
2) Evolutionary theory of sleep
The second theory suggests sleep as a means of conserving energy, a period of inactivity and calm. Contrast with activity, a period of wakefulness that would be the most hazardous. This theory is supported from comparative research of different animal species. Animals that have few natural predators, such as bears and lions, often sleep between 12 to 15 hours each day. On the other hand, animals that have many natural predators have only short periods of sleep, usually getting no more than 4 or 5 hours of sleep each day.
3) Information Consolidation Theory of sleep
Based on cognitive research, this theory suggest that humans sleep in order to process information that has been acquired during the day. Moreover, it argues that zzz prepares the brain for the following day. Sleep is also an integration process of stuff we acquired during the day into long-term memory. Support for this idea stems from a number of sleep deprivation studied demonstrating that a lack of sleep has a serious impact on the ability to recall and remember information.
At the end of the article, Kendra wrote that while there is no crystallized, 'clear-cut' support for any one possible theory, each of these theories could be used to explain why we sleep.
