Psychology -> Area of Study 3 - States of Consciousness -> Sleep -> Purpose of sleep: restoration and survival
Purpose of sleep: restoration and survival
Rechtschaffen's device designed to deprive rats of sleep.
Psychologists have put forward several theories as to why we sleep however, two popular theories are the restoration (restorative) theory and the survival theory.
According to the restorative theory, we need sleep for physical growth and repair of the body. Sleep allows damaged cells to be repaired and muscles to rid themselves of waste products. This theory also maintains that sleep assists with brain growth and restoration. Most of this restoration takes place during stages 3 and 4 of sleep. This theory is supported by research which shows that people engaged in vigorous physical activity sleep longer.
The restorative theory of sleep has a few limitations. These are that:
inactive people such as the disabled, do not necessarily sleep less than more active people;
it is not clear what, if anything, is restored and repaired during sleep;
during sleep we experience a fall in body temperature and metabolic rate which indicates that the body is conserving energy rather than restoring or rejuvenating itself.
The survival theory of sleep suggests that sleep serves as a protective behaviour where the organism is inactive at the most dangerous time of the day. Sleep is therefore an adaptive process, evolved from our ancestors who needed to remain hidden at night to minimise attracting attention from predators at their most vulnerable time. Also, this theory proposes that sleep serves to preserve energy, or reduce heat loss at night by a lowered physical activity level.
However, a main criticism of the survival theory of sleep is that when asleep, an animal is less alert and potentially more vulnerable to attack by predators.