Functional link between distal vasodilation and sleep-onset latency?

Thermoregulatory processes have long been implicated in initiation of human sleep. The purpose of this study was to evaluate the role of heat loss in sleep initiation, under the controlled conditions of a constant-routine pro tocol modified to permit nocturnal sleep. Heat loss was indirectly measured by means of the distal-to-proximal skin temperature gradient (DPG). A step wise regression analysis revealed that the DPG was the best predictor varia ble for sleep-onset latency (compared with core body temperature or its rat e of change, heart rate, melatonin onset, and subjective sleepiness ratings ). This study provides evidence that selective vasodilation of distal skin regions (and hence heat loss) promotes the rapid onset of sleep.