Direct activating effect of the lateral preoptic region of the hypothalamus on the synchronizing system of the thalamus.

Chronic studies on cats were used to analyze rearrangements of total bioelectrical activity and neuron responses in the median center of the thalamus to electrical stimulation of the lateral preoptic nucleus of the hypothalamus. These electrophysiological studies established the existence of ipsi- and contralateral projections from the preoptic region to the median center. The preoptic region was shown to have an activating effect on the thalamic mechanisms generating spindle activity. It is suggested that the preoptic region with the nonspecific thalamus, acting via direct hypothalamo-thalamic connections, is one of the mechanisms involving the preoptic somnogenic system in the initiation of sleep and in the formation of the slow-wave phase of sleep.