General anesthesia and sleep: like and unlike.

General anesthesia and sleep have long been discussed in the neurobiological context owing to their commonalities, such as unconsciousness, immobility, non-responsiveness to external stimuli, and lack of memory upon returning to consciousness. Sleep is regulated by complex interactions between wake-promoting and sleep-promoting neural circuits. Anesthetics exert their effects partly by inhibiting wake-promoting neurons or activating sleep-promoting neurons. Unconscious but arousable sedation is more related to sleep-wake circuitries, whereas unconscious and unarousable anesthesia is independent of them. General anesthesia is notable for its ability to decrease sleep propensity. Conversely, increased sleep propensity due to insufficient sleep potentiates anesthetic effects. Taken together, it is plausible that sleep and anesthesia are closely related phenomena but not the same ones. Further investigations on the relationship between sleep and anesthesia are warranted.