Gamma band activity in the reticular activating system

Abstract

This review considers recent evidence showing that cells in three regions of the reticu-lar activating system (RAS) exhibit gamma b activity, describes the mechanisms behind such manifestation. Specifically, we discuss how cells in the mesopontine peduncu-lopontine nucleus (PPN), intralaminar parafascicular nucleus (Pf), pontine subcoeruleus nucleus dorsalis (SubCD) all fire in the beta/gamma b range when maximally activated, but no higher.The mechanisms behind this ceiling effect have been recently elucidated.We describe recent findings showing that every cell in the PPN have high-threshold, voltage-dependent P/Q-type calcium channels that are essential, while N-type calcium channels are permissive, to gamma b activity. Every cell in the Pf also showed that P/Q-type N-type calcium channels are responsible for this activity. On the other h, every SubCD cell exhibited sodium-dependent subthreshold oscillations. A novel mechanism for sleep-wake control based on well-known transmitter interactions, electrical coupling, gamma b activity is described. The data presented here on inherent gamma b activity demonstrates the global nature of sleep-wake oscillation that is orchestrated by brainstem-thalamic mechanism, questions the undue importance given to the hypo-thalamus for regulation of sleep-wakefulness.The discovery of gamma b activity in the RAS follows recent reports of such activity in other subcortical regions like the hippocam-pus cerebellum. We hypothesize that, rather than participating in the temporal binding of sensory events as seen in the cortex, gamma b activity manifested in the RAS may help stabilize coherence related to arousal, providing a stable activation state during wak-ing paradoxical sleep. Most of our thoughts actions are driven by pre-conscious processes. We speculate that continuous sensory input will induce gamma b activity in the RAS that could participate in the processes of pre-conscious awareness, provide the essential stream of information for the formulation of many of our actions.Copyright © 2012 Urbano, Kezunovic, Hyde, Simon, Beck Garcia-Rill.