AUTHOR=Mashour George A. , Hudetz Anthony G. TITLE=Bottom-Up and Top-Down Mechanisms of General Anesthetics Modulate Different Dimensions of Consciousness JOURNAL=Frontiers in Neural Circuits VOLUME=11 YEAR=2017 URL=https://www.frontiersin.org/journals/neural-circuits/articles/10.3389/fncir.2017.00044 DOI=10.3389/fncir.2017.00044 ISSN=1662-5110 ABSTRACT=

There has been controversy regarding the precise mechanisms of anesthetic-induced unconsciousness, with two salient approaches that have emerged within systems neuroscience. One prominent approach is the “bottom up” paradigm, which argues that anesthetics suppress consciousness by modulating sleep-wake nuclei and neural circuits in the brainstem and diencephalon that have evolved to control arousal states. Another approach is the “top-down” paradigm, which argues that anesthetics suppress consciousness by modulating the cortical and thalamocortical circuits involved in the integration of neural information. In this article, we synthesize these approaches by mapping bottom-up and top-down mechanisms of general anesthetics to two distinct but inter-related dimensions of consciousness: level and content. We show how this explains certain empirical observations regarding the diversity of anesthetic drug effects. We conclude with a more nuanced discussion of how levels and contents of consciousness interact to generate subjective experience and what this implies for the mechanisms of anesthetic-induced unconsciousness.