the human brain remains highly responsive to sound during sleep, but it does not receive feedback from higher order areas — sort of like an orchestra with “the conductor missing.”
“At that time, it was just a wild idea, […] that instead of just a loss of consciousness, anesthetics may do something to the brain that actually turns pain off.”
In “Life As No One Knows It,” Sara Imari Walker explains why the key distinction between life and other kinds of “things” is how life uses information.