Some theories of sleep are based on the knowledge that vigilance levels drop the longer one stays awake. sleep rebound effects (increases in REM and/or non-REM (NREM) sleep following sleep deprivation) occur in an attempt to make up for sleep loss and to restore vigilance.

these theories propose that while one is awake some substance(s) is being depleted or that cells suffer over-exertion. consequently, sleep occurs so that the substance(s) can be restored or so that cells can rest. A problem with this theory is that the "sleep factor" which is hypothetically depleted has never been identified and there is no evidence

these theories focus on the regulation of energy. sleep deprivation experiments have demonstrated that rats who have not been allowed any sleep eventually lose the ability to control their body temperature or maintain their weight and eventually die (loss of control over metabolism and homestasis). therefore certain researchers have proposed that sleep may help to reduce energy disequilibrium by maintaining the efficiency of brain mechanisms that function to regulate energy.

this is another brain plasticity theory which assumes that many behaviours have a large genetic component. these behaviours are present at birth, but usually require adjustment or have a learned component as well, as such, sleep provides the opportunity for these behaviours to be rehearsed. One example of this type of behaviour is the predatory behaviour of the house cat. even though these animals have never had to hunt, prdatory behaviour can be experimentally induced by implanting electrodes into brain regions resp

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Approximate Word count = 670
Approximate Pages = 3 (250 words per page double spaced)