A THERMOREGULATORY MODEL OF SLEEP CONTROL

We hypothesize that non-rapid-eye-movement sleep (NREM) is controlled by thermoregulatory mechanisms of the preoptic/anterior hypothalamus. Circadian and homeostatic thermoregulatory processes may be integrated in this brain area. To investigate this hypothesis, we have developed a mathematical model of qualitative features of human sleep-waking be havior based on a thermoregulatory feedback control mechanism, with mo dulation by two circadian oscillators, one a temperature rhythm, the o ther modulating sleepiness. Homeostatic features of the sleep rhythm a re generated by integration of a heat load associated with waking. Sim ulations under entrained conditions show that the model closely mimick s typical features of human sleep rhythms, including a biphasic daily pattern of sleepiness and sleep-onsets and awakenings fixed in a desce nding phase and an ascending phase of the temperature rhythm, respecti vely. Sleep duration is strongly controlled by the phase difference be tween the two oscillators with the same period; these could represent two phase-differentiated expressions of a single oscillator. In additi on, the simulation of sleep deprivation provides a natural interpretat ion of the experimentally observed phenomena, which shows that the hom eostatic and the oscillatory aspects of the human circadian system is successfully integrated in our model. The promising results obtained s uggest that the control of sleep-wake rhythm could be understood withi n the framework of the thermoregulation.