[The restructuring of the neuronal activity of the lateral hypothalamic preoptic area during the development of sleep].

Activity of neurons of hypothalamic lateral preoptic area was studied in cats during wakefulness, drowsiness and slow-wave sleep. It was shown that development of sleep was accompanied by changes either in frequency and pattern or only in frequency of pulse activity. Neurons which increased their firing rate retained their initial activity pattern characteristic for wakefulness (continuously arrhythmic or burst firing) throughout all sleep stages. The majority of neurons which decreased their firing frequency changed their pattern of activity during drowsiness or SWS. Continuously arrhythmic activity changed for a mixed-type (combination of single-pulse and burst discharges), and mixed-type activity changed for bursting. During SWS substantial part of neurons displayed changes in activity which were phased-locked with sleep spindles. The results support the existence of somnogenic neuronal populations in the preoptic area which participate in the central mechanisms of transition from wakefulness to sleep and formation of the slow-wave phase.