Apical Function in Neocortical Pyramidal Cells: A Common Pathway by Which General Anesthetics Can Affect Mental State.

General anesthetics may suppress either the level of consciousness (arousal) or its contents (specific percepts, thoughts, feelings). This distinction is important for understanding both anesthesia and the neural bases of consciousness. Evidence indicates that both level and content depend on apical input to neocortical pyramidal cells, which selectively amplifies relevant signals. What these cells transmit information about can be separated from arousal levels controlled by sub-cortical nuclei and from prioritization set by thalamocortical interactions. The authors hypothesize that when conscious, we have particular directly experienced mental states, and that anesthetics disrupt the subcellular processes that selectively amplify contextually relevant activities.

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Abstract

It has been argued that general anesthetics suppress the level of consciousness, or the contents of consciousness, or both. The distinction between level and content is important because, in addition to clarifying the mechanisms of anesthesia, it may help clarify the neural bases of consciousness. We assess these arguments in the light of evidence that both the level and the content of consciousness depend upon the contribution of apical input to the information processing capabilities of neocortical pyramidal cells which selectively amplify relevant signals. We summarize research suggesting that what neocortical pyramidal cells transmit information about can be distinguished from levels of arousal controlled by sub-cortical nuclei and from levels of prioritization specified by interactions within the thalamocortical system. Put simply, on the basis of the observations reviewed, we hypothesize that when conscious we have particular, directly experienced, percepts, thoughts, feelings and intentions, and that general anesthetics affect consciousness by interfering with the subcellular processes by which particular activities are selectively amplified when relevant to the current context.