Outline and Evaluate Restoration Theories of the Function of Sleep
There are two influential restoration theories of sleep and they both suggest that sleep serve a restorative function. Starting with Oswaldâs 1980 restoration model, where he proposed that the high level of brain activity during REM sleep reflects brain recovery, with an increase in the bodyâs hormone activities e.g. growth hormone (which serves an important role in protein synthesis) during SWS reflects restoration and recovery in the body and this is supported by the high proportion of REM sleep seen in newborn baby.
On the other hand, Horneâs 1988 core sleep/optional sleep model, which is concluded from a number of controlled laboratory studies that sleep deprivation leads to sleep recovery concentrated in Stage 4 SWS and in REM sleep. He referred these stages as âcore sleepâ as they are essential in humans for the normal brain functioning essential for our cognitive abilities, while the lighter stages of SWS are not essential and he referred them as âoptional sleepâ. The difference between the accounts is that Oswald proposed SWS functions to restore the body to full waking capacity, whereas Horne does not as he believes this occurs during periods of relaxed wakefulness.
The view that sleep has a vital restorative function, however, is weakly supported by research. According to restorative perspective, intense energy expenditure during the day will increase the duration of sleep in order to restore the resources used. However, Breedlove et al. 2007 found that for most people, intense exercise may cause them to fall asleep more quickly but it doesnât cause them to sleep longer. Besides, animals such as sloths have low levels of energy expenditure yet they sleep for about 20 hours a day.
On top of that, sleep deprivation studies have also failed to provide conclusive evidence that sleep is necessary to keep the body functioning normally. Horne 1988 reviewed 50 studies where humans were deprived of sleep and found that very few reported that sleep deprivation had interfered with the participantsâ ability to perform physical exercise. This therefore undermines Oswaldâs claim that sleep serves the function of restoring the body. Moreover, Horne also points out that as amino acids are only freely available for 5 hours after a meal and most people eat several hours before going to bed, then the supply of available amino acids is low for most of the night, hence implying not much protein synthesis would go on during sleep and therefore fails to support the restorative theories that growth hormone is released during SWS which has an important role in protein synthesis. And because of these reasons the restoration theories are limited to prove that sleep does serve a restorative function.
However, the restorative theories are supported by cases where people suffered from a disorder known as fatal familial insomnia. People