Bottom-Up and Top-Down Mechanisms of General Anesthetics Modulate Different Dimensions of Consciousness

Front Neural Circuits. 2017 Jun 20;11:44. doi: 10.3389/fncir.2017.00044. eCollection 2017.

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.

Keywords: anesthesia; anesthetic mechanisms; awareness; connectivity; sleep; unconsciousness; wakefulness.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anesthetics / pharmacology*
  • Animals
  • Brain Mapping*
  • Brain Stem / drug effects
  • Brain Stem / physiology
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / physiology
  • Consciousness / drug effects*
  • Consciousness / physiology*
  • Diencephalon / cytology
  • Diencephalon / physiology
  • Humans
  • Neural Pathways / drug effects*
  • Neural Pathways / physiology*
  • Thalamus / drug effects
  • Thalamus / physiology

Substances

  • Anesthetics