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Contents 1 Functions of Sleep 1.1 Ecological perspective 1.2 Restoration perspective 1.3 Restorative vs ecological? 2 Comments

Functions of Sleep

Ecological perspective

AO1:

• Meddis (1975) believed that sleep behaviour shown by any species depends on their need to adapt to environmental threats and dangers. Sleep serves the function of keeping animals fairly immobile and safe from predators. However, species that are in danger from predators sleep relatively little to remain vigilant.
• Warm blooded animals need lots of energy to maintain body temperature. Animals with high metabolic rates use more energy. Sleep provides a period of inactivity, thereby reducing physiological demands and conserving energy. This is known as hibernation theory (Webb 1982)
• Herbivores eat plants, which are fairly low in nutrients. Therefore they must eat more time eating and consequently less time sleeping. Carnivores eat food that is high in nutrients, so do not need to eat continuously. They can afford to rest and conserve energy.
• Unilateral sleep occurs in animals such as dolphins and birds. One half od the animal’s brain is in NREM at a time, while the other is awake. The two hemispheres of the brain swap every 2-3 hours. In dolphins, this adaptation allows them to surface for air.

AO2:

• Zepelin and Rechtshaffen (1974) studied the relationship between sleep length and metabolic rate across 53 mammalian species. There was a negative correlation between body size and total sleep time, thereby supporting the theory that animals with high metabolic rate sleep for longer. This does not apply to all animals, sloths are large and slow and should not need much sleep, but sleep on average 20 hours a day.
• Allison and Cicchetti (1976) studied relationship between sleep time in their laboratory and degree of danger typically experienced by the species. In 39 species the amount of sleep correlated negatively with danger. However, this does not apply to all species. Rabbits sleep as much as moles, even though rabbits have a much higher danger rating than moles. Both studies demonstrate correlational relationships, rather than causation.
• The ecological theory is difficult to prove false, as animals that are in danger of predation either sleep to keep themselves immobile or stay awake to stay vigilant. It is also hard to apply to human sleep.
• All research is based on observations of animals, but the behaviour of some animals is yet to be recorded.

Restoration perspective

AO1:

• Proposes that sleep is to save energy and permit the restoration of tissue. Oswald identified SWS as being important in the recovery process, and has been linked to release of growth hormone and protein synthesis. Adam and Oswald found that tissue growth of new cells in the skin is quicker when we are asleep.
• Stern and Morgane (1974) suggested that the function of REM sleep is to restore levels of neurotransmitters after each day’s activities. This is supported by evidence that some people on antidepressants show decreased REM, possibly because drugs inhibit their neurotransmitter levels.
• Oswald observed patients recovering from drug overdoses and other injuries to the central nervous system, and found a significant increase in REM activity. Oswald concluded that SWS is important for bodily growth and repair, while REM is important for brain restoration.
• Horne (1988) elaborated on Oswald’s idea. He said that core sleep (SWS and REM) is essential for normal brain functioning, whereas the lighter stages of REM are optional.
• Naitoh discussed various studies concerned with the effects of sleep deprivation on mood. Sleep deprived individual’s described themselves as less friendly, relaxed and good natured and cheerful as those who had not been sleep deprived.
• Berry and Webb assessed self reported anxiety. When people slept well during a given night, their levels of anxiety on the following day were lower than when they had slept poorly.

AO2

• The notion that SWS may be related to protein synthesis is inconsistent. Bentley (2000) argued that SWS is not linked to restoration via protein synthesis. Protein synthesis requires amino acids, which can be obtained by eating foods containing them. These amino acids are available up to 5 hours after eating. He concluded that as people eat several hours before going to be, protein synthesis is unlikely to occur during sleep.
• However, this is also unlikely, as amino acids are continually produced in the body and are not only obtained by food. There is no significant evidence that protein synthesis does not occur or is strictly restricted to SWS
• Various studies have demonstrated the effects of long term sleep deprivation. Michael Corke suffered from the inherited disease fatal familial insomnia, which causes a lack of sleep. He suffered serious physical and mental decline until he died.
• Rechtschaffen et al (1983) forced rats to remain physically active. If they started to fall asleep, he woke them by rotating a disc. After 33 days, all the rats died.
• However, sleep deprivation may not have been the direct cause of death. It may have been caused by stress or impaired regulation of body temperature.
• There is evidence to support the view that sleep causes depressed mood and increased anxiety, thereby suggesting that sleep has a role in the recovery of some psychological functions.

Restorative vs ecological?

• Sleep is crucial to well being according to restorative, whereas it is much less crucial according to ecological. There are no reports of humans who have managed without sleep.
• Horne (1988) proposed that sleep probably serves different purposes in different species

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