Sleep is believed to function as a means of restoring the biological system to a better working order this is the basis of the restoration theory, Sleep is divided into several different stages such as SWS, and REM sleep, Oswald proposed that each of these sleep stages has a different restorative function. SWS enables the body to repair itself and REM enables brain recovery and memory consolidation.
During slow wave sleep growth hormones are secreted, this stimulates growth and is therefore important during childhood. It is also an important stage in adulthood as it also enables protein synthesis and cell growth to take place; this is vital to the restoration of bodily tissue as it is very fragile and needs constant renewal. Sassin et al (1969) found that when sleep-waking cycles are reversed by 12 hours such as going to sleep in the morning and waking up at night, the release of GH with sleep is also reversed. This shows that GH release is controlled by neutral mechanisms related to SWS. This study is supported by research from Van Cauter and Plat (1996) they found that the amount of GH released correlates with the amount of SWS. Further and more recent research from Van Cauter (2000) showed that the decline of GH in older aged people has also been associated with reduced SWS. This gives credibility and reliability to Sessin’s research however his research was a field study therefore extraneous variables could not be controlled, this study could also not be repeated as the conditioning would change each time due to environmental factors. But this study is high in ecological validity and internal validity as it met its aims in investigating GH release during SWS. Kruger et al (1985) found that lack of SWS has also been associated with reduced functioning of the immune system; antibodies are regenerated during cell growth and protein synthesis, this also adds