The psychotomimetic nature of dreams: an experimental study.

Several theories promote the similarities between dreaming and psychosis, but this has rarely been tested empirically. We assessed dreaming and waking reality using the Psychotomimetic States Inventory, a measure of psychotic-like experience originally designed for drug studies. Twenty participants completed the measure in each of two dream conditions and one waking condition. Dreams were assessed upon waking naturally and also using a movement-activated (actigraph) alarm during the night. Overall, participants reported more quasipsychotic characteristics during dreams (in both conditions) than when awake. This was most marked for paranoia and delusional thinking, but differences were also seen for perceptual abnormalities, mania, and anhedonia. The quality of dream experience seems particularly similar to psychosis in sometimes being highly self-referential and having a paranoid content. Subjective changes to cognition and affect are consistent with alterations in prefrontal cortical activity during REM sleep that mirror those of schizophrenia.