It is the purpose of the proposed research to develop and test specific hypotheses regarding the central control of desynchronized sleep (D) at the level of single neurons by the method of chronic extracellular microelectrode recording. Results in hand indicate that the giant neurons of the cat pontine tegmentum (FTG), a region whose intrinsic anatomy and experimental destruction had suggested a role in D sleep, satisfy better than other cell groups three physiological criteria of a central control system: 1) greater selectivity of discharge during D sleep; (2) earlier anticipatory tonic rate change in transition to D sleep; (3) earlier anticipatory phasic rate change in association with the eye movements of D sleep. Long-term recordings show FTG neuronal activity to be (1) consistently selective across repeated D sleep cycles; (2) stereotyped, for each cell, within each cycle; (3) periodic when a series of cycles is considered. A second cell group located in the region of the locus coeruleus, has discharge properties reciprocal to those of the giant cells. Since the two cell groups are interconnected and may use different transmitters of opposite sign, we have developed and are testing a physiological and mathematical model for sleep cycle control based upon the assumption of reciprocal interaction. The work currently in progress includes simultaneous recording of cells in each nucleus and of microinjection into each nucleus of drugs with known effects upon putative cholinergic and aminergic transmitter systems.