Sleep is a normal activity very important for our well-being. Numerous theories try and explain why organisms sleep. The Recuperative theory of sleep is based on the premise that humans require sleep to rejuvenate and recoup spent energy during the waking period. The Circadian theory opines that the human wake-sleep cycle is a natural cycle modified by the day and night cycle of nature. While the former try and explain sleep in behavioral terms, the latter has a more neurobiological explanation for the phenomenon of sleep. This essay attempts to compare and contrast both theories in an attempt to explain their validity.
The recuperative theory bases its proof on the logic that any animal which stays awake 24 hours without break would expend a tremendous amount of energy and be weakened over time and thus fall prey to other animals. Milton (1994) states that “animals sleep so that physiological and biochemical repairs can take place”. Thus to survive, the animal must sleep to conserve energy, allow new energy to replace the spent energy, and make conditions suitable for growth.
The recuperative theory opines that during the act of sleeping, some biological processes take place that increase the chances of growth and survival. According to many scientists, during stage 4 sleep, the parasympathetic system controlling the digestive system becomes active and the cardiovascular system slows down. By doing so, energy expenditure is reduced while digestion helps restoration of energy in the body.
REM sleep provides another clue why the recuperative theory could be valid. It has been proven that humans enter a more restive state during REM sleep. During this period, the muscles are completely relaxed which helps conserve energy and the subsequent buildup. Sleep scientists have also pointed out that the restful condition during sleep promotes the secretion of growth hormones which is yet another reason for the validity of the recuperative theory. However, recuperative theorists find it difficult to explain why there is rarely any difference in sleep patterns, even if someone exercises very hard.
As per the Circadian theory, the normal wake-sleep cycle is about 25 hours. According to Levinthal (1990), “The regulation of circadian cycles is accomplished by the Suprachiasmatic Nuclei (SCN) in the anterior portion of the hypothalamus—-.” The SCN receives information regarding the period of the day via special optic pathways from the retina and thalamus. A free-running 25-hour cycle then gets modified to tune in to the 24-hour natural day-night cycle.
The Circadian theory gives a good plausible reason as to why humans get ‘Jet lagged’. As we travel across time zones, the human biological clock, attuned to a particular place’s day-night cycle, is upset by the continually changing day-night durations. This leads to disorientation, tiredness, and lack of concentration. The US Air Force Instruction (2006) requires their aircrews to get a minimum of 8 hours of sleep to cater for circadian conflicts.
The validity of the Circadian theory of sleep is well established. All studies in sleep deprivation point to the circadian theory as the valid explanation for why organisms sleep. The circadian theory has official recognition the world over. The International Civil Aviation Organisation (ICAO), and all the Air Forces in the world cite the Circadian theory as a reason for determining mandatory rests periods for aircrews. The Recuperative theory, though compelling in some ways, has not found the kind of acceptance as has the Circadian theory. In my estimation, the Circadian theory definitely holds more water than the Recuperative theory of sleep.
References
Air Force Instruction 11-202, volume 3, 2006. Flying Operations – General Flight Rules. Page 70. Web.
Levinthal, Charles F. (1990). Introduction to Physiological Psychology. New Jersey: Prentice-Hall, Inc. Page 312.
Milton, John. (1994). Recent Functional Theories of Sleep and Dreaming. Web.