Arousal and Gating in Neurology of Impaired Consciousness

The Role of Arousal and "Gating" Systems in the Neurology of Impaired Consciousness

Nicholas D. Schiff and Fred Plum

Journal of Clinical Neurophysiology 17, 438-452 (2000)

Abstract

As reviewed here, several lines of evidence support a selective role for subcortical gating systems in the mechanism of global disorders, apart from the contributions of the arousal systems. The clinical expression of global disorders produced by subcortical injuries may thus depend on whether such selective gating processes are completely or only partially disabled. For example, the vegetative state represents a complete loss of integrative cerberal activity, as does the brief unconscious state accompanying typical absence seizures. In the absence seizure, the loss of gating may result from several, typically only partially dependent, activity envelopes coalescing into a single "brain beat" (analogous to the bursts of generalized theta seen with normal drowsiness). Partial loss of such grating processes would attend hyperkinetic mutism, akinetic mutism, or temporal lobe seizures. In these disorders, preserved but isolated minimal neuropsychological expressions may survive, such as the crude form of attention in akinetic mutism; the uncontrolled, aimless motor intention observed in hyperkinetic mutism; or the automatic behaviors accompanying complex partial seizures. As suggested earlier, the specific gating processes may be identified with activity envelopes organized around important endogenous transient events, such as eye movements or shifts of attention, that are used to facilitate long-range communicaiton in the forebrain. The episodic dynamics of these activity envelopes, operating within the background arousal state, may be faciitated primarily by the gating systems and may organize many different ongoing neuronal assembly processes.

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