Consciousness, Anesthesia, and Acetylcholine

Although the precise neural correlates of consciousness have not yet been identified, there is one neurochemical marker that appears to track with our capacity to experience something: acetylcholine concentration in the cerebral cortex. Cortical acetylcholine concentration is high during wakefulness, decreases during slow-wave sleep, and increases again during rapid eye movement sleep, when we can have the conscious experience of dreaming.¹  Based on the neuropharmacology of the particular anesthetic drug we might choose, the state of general anesthesia shows parallel changes. For example, the effects of the γ-aminobutyric acid–mediated (GABAergic) anesthetics propofol and sevoflurane are similar to slow-wave sleep and include low acetylcholine concentration, slower electroencephalographic frequency, and a low probability of experience.^2,3  By contrast, the effects of the non-GABAergic anesthetics ketamine and nitrous oxide are similar to rapid eye movement sleep and...