Brainstem Ascending Systems Controlling Synaptic Transmission of Afferent Signals

Abstract

We now examine the state dependency of thalamic and cortical neuronal responses to afferent signals and the underlying mechanisms of the enhanced excitability in those neurons during the EEG-desynchronized states of wakefulness and REM sleep compared to EEG-synchronized sleep. Data showing the striking electrophysiological similarities between two behavioral states that were initially considered as two poles of the waking---sleep cycle led to the conclusion that both waking and REM sleep are brain-activated states, notwithstanding great differences in their mental content and despite the fact that central motor commands are blocked at the spinal motoneuronal level during REM sleep. During waking, the increased neuronal responsiveness is associated with an increased efficacy of sculpturing inhibition involved in discriminatory tasks. We examine the control exerted by brainstem ascending systems and their neurotransmitters on both excitatory and inhibitory processes in the thalamus and neocortex. Inhibitory processes have not yet been systematically investigated during REM sleep, and this promising avenue of research may eventually substantiate, at a cellular level, some of the basic psychological differences between the two brain-activated states, otherwise similar from various electrophysiological points of view.