<P> In 1993 , a different model called the opponent process model was proposed . This model explained that these two processes opposed each other to produce sleep , as against Borbely 's model . According to this model , the SCN , which is involved in the circadian rhythm , enhances wakefulness and opposes the homeostatic rhythm . In opposition is the homeostatic rhythm , regulated via a complex multisynaptic pathway in the hypothalamus that acts like a switch and shuts off the arousal system . Both effects together produce a see - saw like effect of sleep and wakefulness . More recently , it has been proposed that both models have some validity to them , while new theories hold that inhibition of NREM sleep by REM could also play a role . In any case , the two process mechanism adds flexibility to the simple circadian rhythm and could have evolved as an adaptive measure . </P>
<P> In 1993 , a different model called the opponent process model was proposed . This model explained that these two processes opposed each other to produce sleep , as against Borbely 's model . According to this model , the SCN , which is involved in the circadian rhythm , enhances wakefulness and opposes the homeostatic rhythm . In opposition is the homeostatic rhythm , regulated via a complex multisynaptic pathway in the hypothalamus that acts like a switch and shuts off the arousal system . Both effects together produce a see - saw like effect of sleep and wakefulness . More recently , it has been proposed that both models have some validity to them , while new theories hold that inhibition of NREM sleep by REM could also play a role . In any case , the two process mechanism adds flexibility to the simple circadian rhythm and could have evolved as an adaptive measure . </P>
area of the brain that regulates sleep-wake cycles
area of the brain that regulates sleep-wake cycles
hypothalamus
hypothalamus