Functions of sleep: Restoration theory

Restoration theory- Many different stages of sleep,incl.SWS and REM-Oswald proposed that SWS enables body repair and REM enables brain recovery.

SWS- Growth hormone secreted in pulses during day but significant amount released during SWS- Vital in restoration of body tissue because proteins are fragile and must constantly be renewed.Restoration of vital proteins part of body's natural recovery process.Sassin et al found that sleep waking cycles are reversed by 12hours the release of GH with sleep is also reversed, thus GH is controlled by neural mechanisms related to SWS.Further evidence- Van Cauter & Plat found that the amount of GH released correlates with amount of SWS and the decline of GH in older age has also been associated with reduced SWS.

The immune system- Krueger et al found that lack of SWS has been associated with reduced functioning of the immune system. the immune system consists of various protein molecules which are regenerated during cell growth and protein synthesis in SWS.

Brain growth-It has been suggested that the amount of REM sleep in any species is proportional to the immaturity of the offspring at birth.eg.Siegel found- platypus is immature at birth and has about 8hours REM sleep, whereas dolphin which can swim from birth, has almost no REM sleep, suggesting a relationship between neural development and REM sleep.

Neurotransmitter activity may be affected by REM sleep.Siegel and Rogawski suggest REM sleep allows break in neurotransmitter release which permits neurons to regain their sensitivity to allow the body to function properly.Support from antidepressant drugs such as MAOI's-they aim to increase levels of neurotransmitters(dopamine and serotonin).A side effect is that MAOI's aboloish REM sleep.Suggestion that the two effects are linked- increase in monoamines means that monoamine receptors dont have to be revitalised,thus no need for sleep.

REM and memory- Crick and Mitchison proposed that during REM sleep,unwanted memories are discarded,making more important memories accessible.Recent research has found more complex relationship.Evidence suggests that REM is consolidation of procedural memory,while SWS is important for consolidation of semantic memory.

Effects of sleep deprivation- if sleep has important restorative effects then sleep deprivation should have clear consequences.

Effects of total sleep deprivation-+ American dj stayed awake for 201hours.Three days in he became unpleasant & abusive.After 5days he began to hallucinate and become paranoid.He showed continuous decline in body temp and by the end his waking brain patterns were the same as those of a sleeping person.-After 24hours of sleep he reported himself perfectly normal.American student also stayed awake for 260hours with no display of psychotic symptoms and was also perfectly normal after lenghty sleep.The studies suggest lack of sleep doesnt always result in long-term damage and no need to recover anything near the amount that was lost.+However,William et al found when P's have been deprived for more than 72hours being closely monitered,they had short periods of microsleep, non sleepers are gettin benefits of sleep while being awake.Vietnamese man stopped sleeping in 1973 with no ill affects.Studies of non-human animals suggest sleep deprivation can be fatal.Rechtshaffen et al kept rats awake by turning the disc they were on everytime they began to sleep.after 33days all rats died.

Partial sleep deprivation-+ If people are deprived specifically of REM sleep, they may experience REM rebound- when they next go to sleep they have an incresed tendency to go into REM sleep, on recovery nights the proportion of REM sleep increases to upto 50% more than usual(Empson).

Excerise and need for sleep- +After excersise you should need extra sleep for body repair. Shapiro found that runners in a marathon slept for about an hour or more on the two nights following the race-SWS increased in particular, which fits the view that NREM sleep appears o be more associated with physical recovery.-However, Horne and Minard gave participants numerous exhausting tasks to see if this increased sleep duration,but it didnt. P's went to sleep faster than usual but not for longer.

case studies(-)-Individual case studies give us most information about sleep but the participants tend to be unique as someone with sleeping difficulties is less likely to volunteer for a studies and people who do volunter will be highly motivated to cope with sleep deprivation.-This research is not representative of the population at large.

Animal research- Other research has used animals because of ethical issues in depriving people of sleep.Animals have different requirements and sleep patterns to humans and therefore may not be generalisable to humans.

This theory does not take into account an evolutionary perspective which suggests that we sleep to prepare for potential dangers.