The restoration theory says we sleep to restore the body’s ability to function at the end of the day.
Oswald said that short-wave sleep (SWS) is for restoring the body in terms of physical activity, whilst REM sleep is for resting the brain functions.
A strong link has been found between growth hormone (GH) and tissue repair. Research has found that GH levels are steady throughout the day but then much higher at night. Also, Sassin et al found that when people changed their sleeping patterns to sleep during the day and stay awake at night the levels of GH also changed. All this suggests a link between sleep and physical restoration.
A lack of SWS has also been linked with a reduced function of the immune system (Krueger et al). This supports the view that sleep helps restore the body physically because the immune system consists of protein molecules which as regenerated during cell growth in SWS.
Also Shapiro found that long-distance runners had more SWS after a race, suggesting that the exercise increased the need for bodily restoration.
Babies brains grow extremely rapidly as they learn more about the world. So the fact that babies also have a much higher percentage of REM sleep suggests that REM sleep and brain restoration are linked. This link is also found in the animal kingdom. For example a dolphin, which is very mature from birth, requires very little REM sleep whereas a platypus, which is very mentally immature from birth, has almost 8 hours of REM sleep.
Also a link has been suggested between REM sleep and memory. Crick and Mitchison proposed that during REM sleep unwanted memories are discarded, meaning we only have the memories we really need, making our brain more ‘efficient’.
Evaluation of the restoration theory
The effects of total sleep deprivation – American DJ Peter Tripp stayed awake for 201 hours for charity. 3 days into the experiment Tripp became abusive, and after 5 days he began to hallucinate. This suggests that sleep does have a restorative function as without it Tripp’s body began to degrade.
However, an American student Randy Gardner stayed awake for 260 hours and suffered no ill effects. This disputes the restoration theory because Gardner went without sleep for 11 days and still didn’t need ‘restoring’.
Exercise and sleep – if the restoration theory is true we should also see an increased need for sleep, in particular SWS, as we look to restore the body after intense exercise. Shapiro’s study as mentioned early supports this as it showed long distance runners require more SWS after a race. However, little other research provides the same conclusion. This suggests that perhaps the link between SWS and restoring the body isn’t a clear as we first thought.
Why do we need to be unconscious to sleep? – Many animals such as dolphins and seals never fall unconscious to sleep and have very little REM sleep. This questions the restoration model as, firstly, if some animals don’t need REM sleep but still have sound mental health does REM really restore us mentally? And secondly, why do we need to fall unconscious to sleep? This second question is why some psychologists suggests there are other reasons for sleep, including environmental pressures.