A cooperative study on the nature of consciousness—between the University of São Paulo and the University of Wisconsin(Madison)—appears to indicatethat unconsciousness is what happens when different parts of the brain can’t connect:

"The [reserachers] compared the brain activity of patients from the full spectrum of consciousness — awake, asleep, drugged with anesthetics, in comas or suffering from “locked-in syndrome,” in which the body appears trapped in a comalike state but the brain is active and aware. "