Anesthesia and sleep have much in common, particularly where breathing is concerned. This relationship is based on the similarities in physiological changes that occur with transition from consciousness to unconsciousness in each state. Wakefulness stimulates breathing through non-specific excitatory activity mediated through the ascending arousal system. Recent evidence suggests that the parabrachial complex, a component of this system, has key roles in both the generation of wakefulness and in the patterning of breathing during it. This activity diminishes with loss of consciousness, whether at induction of anesthesia or at sleep onset.

The neurophysiological pathways involved in transition from wakefulness to sleep are activated by anesthetic drugs and so are deeply implicated in the mechanisms of anesthesia. Given this, it is perhaps not surprising that similar physiological changes occur with loss of consciousness in both states. Volition...

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