The Head Trip: Adventures on the Wheel of Consciousness

release of growth hormone. It’s in slow-wave sleep that the body does its growing. In young children, new bone and tissue get built; in everyone, regardless of age, damaged tissue gets repaired. The immune system may also get a boost

references to a “second” or “morning” sleep. The picture he began to piece together of human sleep before the industrial era was not one anyone had ever remarked on before. It appeared that people slept in two bouts: an evening bout, which lasted from about 9 p.m. to sometime after midnight, and a morning bout, which lasted from around 2 a.m. to da

What is a “state” of consciousness? A lot of ink has been spilled on this question; for our purposes, it can be thought of as a kind of background level of awareness. In consciousness theorist Bernard Baars’s well-known formulation, it’s a “global workspace” in which the contents of consciousness—the visuals, auditory activity, thoughts—are all on