The role of the medial preoptic area of the hypothalamus in organizing the paradoxical phase of sleep.

Chronic experiments were performed on cats to study the effects of electrical stimulation of the medial preoptic area of the hypothalamus on the latent period, duration, and structure of paradoxical sleep, as well as the dynamics of neuron activity in this structure during the sleep-waking cycle. These investigations showed that low-frequency stimulation of the medial preoptic area during slow-wave sleep led to short-latency development of desynchronization of bioelectrical activity in the neocortex and initiated the development of paradoxical sleep or a similar state. Stimulation of this structure during paradoxical sleep led to a decrease in its duration, to the virtually complete disappearance of the tonic stage of paradoxical sleep, and to an increase in the frequency of rapid eye movements in the phasic stage. Rearrangement of neuron activity in the medial preoptic area during the sleep-waking cycle was similar to that seen in cells of the lower brainstem "executive" centers of paradoxical sleep. It is suggested that neurons in the medial preoptic area of the hypothalamus are actively involved in the mechanisms of paradoxical sleep and, in particular, in the desynchronization of neocortical bioelectrical activity which develops during this stage.