 Dreams are a global state of consciousness in which experience arises under altered behavioral and neurophysiological conditions as compared to standard wakefulness; unlike other altered states of consciousness (such as drug-induced or deep meditative states) and pathological wake states (such as psychosis or neurological syndromes), dreams occur spontaneously and regularly in healthy subjects. For both reasons, many regard dreams as a test case for theories of consciousness or even an ideal model system for consciousness research (Churchland 1988; Revonsuo 2006).