Cellular and Microcircuit Mechanisms of Anesthetic Disruption of Conscious-State Organization.

The reversible effects of general anesthesia can be used to examine how brain activity changes during transitions into and out of altered conscious states. Such changes are commonly tracked using behavioral responses, electroencephalographic recordings, and measures of functional connectivity. These measures, however, reflect processes occurring at lower levels of organization, including the activity of pyramidal neurons, dendritic integration, interneuron function, thalamocortical signaling, and glial regulation of the extracellular environment. Anesthesia does not affect all neural processes equally. Propofol and volatile agents interfere with synaptic transmission and apical dendritic integration, as well as cortical feedback and thalamocortical signaling. The resulting activity is not necessarily absent or uniformly weaker. It is often more stereotyped, temporally restricted, and poorly coordinated between regions. Ketamine produces a different organization. Substantial neural activity and complex cortical responses may persist after behavioral responsiveness has been lost, although deeper anesthesia also produces slower and less complex activity. Responsiveness, environmental connectedness, memory, reportability, and conscious content may therefore become partly uncoupled. Ketamine produces a dissociative state that cannot be interpreted simply as another form of the predominantly restrictive state produced by propofol or volatile anesthetics. This narrative review synthesizes evidence identified through a structured PubMed search to examine how anesthesia reshapes conscious processing and why unresponsiveness or absent recall may not indicate absent experience.