Consciousness and Anesthesia

Abstract

When we are anesthetized, we expect consciousness to vanish. But does it always? Although anesthesia undoubtedly induces unresponsiveness and amnesia, the extent to which it causes unconsciousness is harder to establish. For instance, certain anesthetics act on areas of the brain’s cortex near the midline and abolish behavioral responsiveness, but not necessarily consciousness. Unconsciousness is likely to ensue when a complex of brain regions in the posterior parietal area is inactivated. Consciousness vanishes when anesthetics produce functional disconnection in this posterior complex, interrupting cortical communication and causing a loss of integration; or when they lead to bistable, stereotypic responses, causing a loss of information capacity. Thus, anesthetics seem to cause unconsciousness when they block the brain’s ability to integrate information.

Effects of the anesthetic agent propofol on neural populations

“…These differences may yield hysteresis effects in the anesthetic action (Dutta et al 1997). More recent studies examined the direct action of AA on single neurons (Antkowiak 1999;Franks and Lieb 1994) and synaptic and extrasynaptic receptors (Franks 2008;Hemmings Jr. et al 2005;Orser 2007;Bai et al 1999;Alkire et al 2008). In this context one of the most important findings is the AAs weakening action on excitatory synaptic receptors and the enhancement of inhibitory synaptic activity.…”

“…For instance, immobility is assumed to be generated in the spinal cord (Rampil and King 1996), and the dorsolateral prefrontal cortex and the thalamus are affected during amnesia (Veselis et al 1997). Similarly the underlying mechanism of the loss of consciousness and its spatial location is unknown though some studies point out the importance of the thalamus (Carstens and Antognini 2005;Alkire et al 2008;Stienen et al 2008). The present work focusses on the loss of consciousness (LOC) and aims to model corresponding experimental findings.…”

“…In the following we discuss briefly this question. On one hand it is well-known that single brain areas play an important role, such as the thalamus (Carstens and Antognini 2005;Alkire et al 2008) which generates spindle waves close to the point of LOC. Since the thalamus is the gateway for sensory information in the brain, GA appears as a network effect mainly triggered by the thalamic action.…”

The Role of Dendritic Signaling in the Anesthetic Suppression of Consciousness

“…How are the brain's computational processes affected by this and other molecular mechanisms of anesthetics, so that patients undergoing surgery cease to experience their surrounds in terms of sight, sound, and touch? Anesthesiologists and cognitive neuroscientists alike have been captivated by these questions and have proposed a number of models in an attempt to answer them, such as Flohr's "information processing theory of anesthesia," 2 Alkire's "thalamic consciousness switch hypothesis," [3][4][5][6] Mashour's "cognitive unbinding paradigm," 7,8 John and Prichep's "anesthetic cascade," 9 or Hudetz's "forgotten present." 10,11 We shall return to some of these frameworks in a later section of the article.…”

“…So in order to publish this adaptation, authorization must be obtained both from the owner of the copyright in the original work and from the owner of copyright in the translation or adaptation. Kaspar Meyer A Dendritic Signaling Hypothesis of Anesthesia others 5,29 have proposed that a disruption of corticocortical top-down processing may play a causal role in the anesthetic suppression of consciousness. This suggestion raises two immediate questions: First, at which anatomical site, and by virtue of which physiological mechanism, do general anesthetics interfere with top-down signaling?…”