Dreaming in the late morning: summation of REM and diurnal cortical activation.
Consciousness and Cognition September 1, 1995 J Antrobus, T Kondo, R Reinsel et al.
Dreaming is more intense during REM sleep than other sleep stages, but it remains unclear whether the brief, phasic events of REM or its sustained, tonic background activation are responsible for features like visual vividness, narrative shifts, and incongruities. This experiment sampled reports of imagery and thought during spontaneous variations within the REM-NREM cycle and across the 24-hour diurnal rhythm, manipulating sleep and wake times to separate their effects. Results suggest that the main driver of vivid visual imagery and enhanced cognitive activity during sleep is a pattern of subcortical and cortical activation common to both the REM phase and the activated (waking) phase of the diurnal cycle.