CHANGES IN NEURONAL-ACTIVITY OF HYPOTHALA MIC LATERAL PREOPTIC AREA ACCOMPANYING DEVELOPMENT OF SLEEP

Activity of neurons of hypothalamic lateral preoptic area was studied in cats during wakefulness, drowsiness and slow-wave sleep. It was sho wn that development of sleep was accompanied by changes either in freq uency and pattern or only in frequancy of pulse activity, Neurons whic h increased their firing rate retained their initial activity pattern characteristic for wakefulness (continuously arhythmic or burst firing ) throughout all sleep stages. The majority of neurons which decreased their firing frequence changed their pattern of activity during drows iness or SWS. Continuously arhythmic activity changed for a mixed-type (combination of single-pulse and burst discharges), and mixed-type ac tivity changed for bursting. During SWS substantial part of neurons di splayed changes in activity which were phase-locked with sleep spindle s. The results support the existence of somnogenic neuronal population s in the preoptic area which participate in the central mechanisms of transition From wakefulness to sleep and formation of the slow-wave ph ase.