Restoration theory suggests that the function of sleep is to repair or restore the brain and body to peak condition. Sleep is therefore related to the demands placed on the brain and body (growth, exersion, damage etc)
- Williams et al (1959) found that it was impossible to prevent microsleep in piolts beyond 72 hours of sleep deprivation. This suggests that sleep is very important to the bodies survival that the brain forces the body to sleep. This supports restoration theory and is supported by cases like Peter Tripp.
- Peter Tripp deprived himself of sleep for 201 hours during which he showed a dramatic decrease in his mental well being and left him with a perminant personality change. This suggests that sleep has an essential role in restoring the bodies essencial functions. During the period of sleep deprivation Tripp experienced vivid hallucinations which, when his brain waves were studied , showed a simularity to REM sleep, suggesting that REM sleep is so important that the brain forces the body into it even during waking hours.
Oswald developed this basic idea by suggesting that 'slow wave sleep' (SWS - stages 3 & 4) and REM sleep, may have different restorative functions.
- SWS allows growth and repair of the body.
- REM sleep allows for growth, repair and restoration of the brain.
- Green (1994) observed the sleep of new born infants and found that they spend a very high proportion of their sleep in REM, during which time infants undergo major development, particularly of the brain. This suggests that the main function of REM sleep is for growth and development. This not only supports Oswald but also the whole idea of restoration theory.
Horne suggested that 'core' sleep (stages 3 & 4 and REM) had a restorative function for the brain and the and that other stages are 'optional sleep'
- Optional sleep allows growth and repair of the body, but no more than restful wakefulness.
- Core sleep allows the growth, repair and reorganisation of the brain.
- Epson (2002), woke participants during REM sleep and found that participants entered REM sleep more quickly after falling back to sleep. This suggests that REM sleep has a higher importance due to the brain spending a greater proportion of time at this stage.
- Wu et al (1999), found that symptoms of depression were actually reduced following selective deprivation of REM sleep. This refutes Horne's theory suggesting that REM sleep has no importance as deprivation of it improves patients condition.
Horn has recently reduced the importance of REM sleep and relabeled optional sleep as elastic sleep. This idea has been criticised by many other psychologists but with other evidence such as some antidepressants appear to remove REM sleep whilst still improving the patient's condition.
Hibernation Theory (Webb, 1982)
Hibernation theory is a ecological theory of sleep that suggests that sleep has the same benefit to animals as hibernation in that being asleep has a survival benefit because it conserves valuable energy through a period of forced inactivity when anything else would be a waste of energy.
- Zepelin & Rechtschaffen (1974), found a negative correlation between body size and total time spent sleeping in 53 mammals. This suggests that animals with higher metabolic rates do sleep for longer supporting restoration theory. However, many of the smaller animals are at greater risk of predication. The study has also only been conducted on a small selection of animals, with other researchers fining may other animals that do not fit this pattern. This suggests that the study lacks reliability.
- It has been found that animals do not conserve mush less energy when sleeping than when awake (only reduced by about 5 - 10 %) this refutes hibernation theory.