Slow rhythmic rate fluctuations of cat midbrain reticular neurons in synchronized sleep and waking

Neuronal rate fluctuations in midbrain reticular formation (MRF) in chronically implanted, behaving cat were analyzed for occurrences of slow rhythmic activity (periods 6–24 s) in quiet waking and synchronized sleep (S). Appreciable rhythmicity, when compared to that resulting from randomly ordered intervals, was found in both vigilance states with rhythmic periods usually between 8 and 12 s. Fifteen MRF neurons having epochs exceeding 2 min in S, and analyzed as a group, suggest the existence of common rhythms related to the onset of S, show a significant rate decrease about 1 min before the end of S, and suggest a possible return of common rhythms relative to the end of the state.