Circadian and ultradian influences on dreaming: A dual rhythm model

The dual rhythm model of dreaming states that, under high sensory thresholds, heightened general cortical activation common to both REM/NREM and circadian-driven activation cycles sums to produce the main characteristics of dreaming. In addition, the unique pattern of regional brain activation characteristic of REM sleep amplifies the emotional intensity of the dream. Subjects were awakened from REM and NREM sleep once near the nadir of the core body temperature rhythm, where circadian-driven cortical activation was assumed to be low, and again in the late morning, where this activation was presumed to be high. As predicted, changes in the central characteristics of dream reports mirrored REM/NREM and circadian-driven fluctuations in general activation, while at the same time, the regional activation pattern unique to REM sleep amplified dream emotionality selectively in REM reports.