Describe and evaluate one theory of the function of sleep (24 marks) Recovery/ Restoration is one theory on the functions of sleep. This theory is based on the concept that sleep is needed to save energy and to allow restoration of tissue. Research evidence that supports this theory focuses mostly around physiological benefits of sleep. Alison and Cicchetti (1976) surveyed 39 mammalian species to work out the amount of time spent in slow wave sleep (SWS) and in REM sleep. It was found that body weight (which correlates with metabolic rate) was the best indicator of the amount of SWS needed.
Oswald’s (1980) findings can relate to this; he found that during SWS growth hormones are released from the pituitary gland, stimulating protein synthesis; which is essential for tissue repair. This can explain why new-borns spend a great deal of time sleeping, due to the fact that REM sleep reflects brain recovery and the few months before and after birth are times of rapid brain growth- babies spend 50-60% of their ‘sleep time’ in REM sleep. Shapiro et al (1981) studied runners who had taken part in an ultra-marathon. They found that the runners slept for around an hour and a half longer than usual for two nights after the marathon.
Also, there was an increase in the amount of time spent in SWS. However, this would suggest that people who do little physical activity would need less sleep than people who do more physical activity, whereas there is no research evidence to support this. The theory also suggests that sleep is essential to psychological well being. This is supported by studies on insomniacs, who tend to be more worried and anxious than people who sleep normally.
However, in these cases it is difficult to establish whether it is people’s concerns and worries disrupting sleep or disrupted sleep-causing worries. Additionally, Naitoh (1975) discusses various studies concerning the effect of one nights sleep deprivation on a person’s mood. The effects were consistently negative (sleep deprived individuals described themselves as less friendly, good natured and relaxed than those who had not been sleep deprived.
Research on long-lasting sleep deprivation in humans has shown that after a period of sleep deprivation, the majority of ‘extra time’ spent in sleep is in stage 4 SWS and REM sleep, as shown in the case of Randy Gardner who after staying awake for 264 hours, spent 15 hours sleeping, in which he recovered two thirds of lost stage 4 SWS and half of lost REM sleep, but little of the other stages of sleep. Horne (1988) proposed that, in humans, stage 4 SWS and REM sleep are the critical phases, known as core sleep, which are essential for brain functioning and the lighter stages of sleep are optional sleep. During core sleep the brain recovers and restores itself after the days’ activities.
This theory suggests sleep is essential to well being, psychological and physiological and there is much research evidence in support of this. Furthermore, sleep deprivation can have fatal consequences, many road and industrial accidents occur as a result of tiredness. However, there is no correlation between amount of physical activity and amount of sleep needed. Furthermore, as animals were used in many of the studies, the results could have been due to stress of participating in the experiment and the methods used to keep the animals awake (ethical issues); as opposed to sleep deprivation.
In conclusion, as Home suggested, sleep may serve different purposes for different species, so while this theory may be sufficient in explaining the functions of sleep in humans, we cannot generalise to all species. For example, in reptiles the cerebral cortex, from which EEG recordings are obtained, is poorly developed and so we cannot study reptilian sleep. Whereas sleep is clearly identifiable in birds and mammals, suggesting it does have an important function. Also, due to differences between species, no single theory does provide a more thorough and well-developed account of sleep than the adaptive or evolutionary theory.