Slow rhythmic oscillations of EEG slow-wave amplitudes and their relations to midbrain reticular discharge

The amplitude of anterior neocortical EEG slow-waves (0.5–4Hz) measured during quiet waking, drowsy (WS) and synchronized sleep (S) states showed slow rhythmic oscillations in WS and S similar to those previously reported in midbrain reticular neurons (periods of 8–12 s). Abrupt changes in slow rhythms of unit discharge was reflected by similar changes in the amplitude of EEG slow-waves. Analyses on grouped data from many WS → S transitions showed no common phase relation between oscillations of EEG slow-wave amplitudes prior to S onset, but showed signs of a common phase relationship after. These findings, together with a significantly lower EEG synchronization level just before S onset in grouped data, suggest that the beginning of S is phase-related to oscillations of slow-wave amplitudes in WS.