The general purpose of this research is to elucidate the neural mechanisms by which the brain controls its own excitability so as to account for the periodic succession of states of consciousness: waking, sleeping, and dreaming. In particular, we aim to test the reciprocal interaction hypothesis of sleep cycle control to determine the cellular changes in the brain during sleep that result in the alteration of the sleeping and dreaming states. The reciprocal interaction hypothesis postulates that the sleep-dream cycle is the result of the contrapuntal oscillation of activity in two classes of brain stem neurons: the pontine reticular neurons (of which the prototype is the giant cell) and the biogenic amine-containing neurons (of which the prototypes are the noradrenergic locus coeruleus cell and the serotonergic dorsal raphe cell). The experiments proposed will test two aspects of the hypothesis and will focus on the generation of the desynchronized phase of sleep: a. A first set of experiments is directed at elucidating which brain stem neurons command the various components of desynchronized sleep (e.g. muscle atonia, EEG activation, PGO waves, and REM's). b. A second set of experiments is directed at the cellular mechanisms by which the excitability of the command elements is modulated throughout the cycle. Significance of the work is seen in its application to three scientific fields which are basic to psychiatry: the relationship of the brain to behavior; the pathophysiology of hallucinoid states; and biological rhythms. We also believe that the approach taken may be useful in the study of other vegetative behaviors and in the development of rational treatment of sleep disorders.