  Humans have employed an incredible variety of plant-derived substances over
the millennia in order to alter consciousness and perception. Among the
innumerable narcotics, analgesics, 'ordeal' drugs, and other psychoactive
substances discovered and used in ritualistic contexts by cultures around the
world, one class in particular stands out not only for its radical
psychological effects, but also for the highly charged political and legal
atmosphere that has surrounded it since its widespread adoption about 50 years
ago: so-called psychedelic substances. We review functional neuroimaging
investigations of the neural correlates of the psychedelic experience, and
highlight relationships with the psychological and neural bases of creativity,
daydreaming, and dreaming.
