Anaesthetics make us unconscious. In sleep we dream. Mystics and others report heightened experiences. Dendrite structure modifications Modification of dendrite structures seems to be associated with conscious experience, but not directly so for the time scales don't appear to match. These phenomena seem normally to be at a low or degraded level of consciousness, yet evidence of their reality mounts.
Subjective aptitude appears to be important.
He is not impressed by theories based on quantum theory. Alwyn Scott's Homepage Physics of Consciousness, by Stapp leads to the first part of a seven-part paper which is a valuable personal review of the topic. Physics of Consciousness by Henry Stapp, Lawrence Berkley Lab. A fascinating subject for me, which seems to be unusual among physical scientists, is the nature of subjective experience. It is such an essential component of life.