Mesopontine Cholinergic Systems Suppress Slow Rhythms and Induce Fast Oscillations in Thalamocortical Circuits

A clear-cut enhancement in amplitude of spontaneous rhythms and their acceleration up to 40 to 45 Hz was seen on cortical EEG, simultaneously with the ocular syndrome of arousal, regardless of the frequency of stimulation applied to the brainstem core.

Abstract

The terms synchronization and desynchronization have been coined for highamplitude and slow ( 20 Hz) waves during arousal and sleep with dreaming episodes. This dichotomy, used because of its heuristic value, simplifies a more complex reality. Indeed, sequences of fast oscillations may occur with much higher amplitudes than those of background activity during states of increased vigilance. This phenomenon was first observed by Bremer et al. (1960), who emphasized that a flattening of the cortical electroencephalogram (EEG) on brain stem reticular stimulation (Moruzzi and Magoun, 1949) is not the only effect of this now classical experimental way of mimicking awakening. Instead, a clear-cut enhancement in amplitude of spontaneous rhythms and their acceleration up to 40 to 45 Hz was seen on cortical EEG, simultaneously with the ocular syndrome of arousal, regardless of the frequency of stimulation applied to the brainstem core (see Fig. 5C—D in Bremer et al., 1960).