Dreaming is characterized by formal visual imagery (akin to hallucination), by inconstancy of time, place, and person (akin to disorientation), by a scenario-like knitting together of disparate elements (akin to confabulation), and by an inability to recall (akin to amnesia). Taken together, these four dream features are similar to the delirium of organic brain disease. By studying the brain during rapid-eye-movement (REM) sleep-the phase of sleep in which most dreaming occurs-we can begin to understand its basis in the altered neurophysiology of REM.