Elsevier

Consciousness and Cognition

Volume 9, Issue 3, September 2000, Pages 370-386
Consciousness and Cognition

Target Article
Toward a Unified Theory of Narcosis: Brain Imaging Evidence for a Thalamocortical Switch as the Neurophysiologic Basis of Anesthetic-Induced Unconsciousness

https://doi.org/10.1006/ccog.1999.0423Get rights and content

Abstract

A unifying theory of general anesthetic-induced unconsciousness must explain the common mechanism through which various anesthetic agents produce unconsciousness. Functional-brain-imaging data obtained from 11 volunteers during general anesthesia showed specific suppression of regional thalamic and midbrain reticular formation activity across two different commonly used volatile agents. These findings are discussed in relation to findings from sleep neurophysiology and the implications of this work for consciousness research. It is hypothesized that the essential common neurophysiologic mechanism underlying anesthetic-induced unconsciousness is, as with sleep-induced unconsciousness, a hyperpolarization block of thalamocortical neurons. A model of anesthetic-induced unconsciousness is introduced to explain how the plethora of effects anesthetics have on cellular functioning ultimately all converge on a single neuroanatomic/neurophysiologic system, thus providing for a unitary physiologic theory of narcosis related to consciousness.

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    Address correspondence and reprint requests to Michael T. Alkire, University of California, Irvine Medical Center, Department of Anesthesiology, 101 City Drive South, Building 53, Route 81-A, Orange, California 92668. Fax: (714) 456-7702. E-mail: [email protected].

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