Regional cerebral blood flow during light sleep--a H(2)(15)O-PET study.
Journal of Sleep Research September 1, 2002 Troels W Kjaer, Ian Law, Gordon Wiltschiøtz et al.
During stage-1 sleep (somnolence), regional cerebral blood flow increases in the occipital lobes and decreases in the bilateral cerebellum, bilateral posterior parietal cortex, right premotor cortex, and left thalamus, compared to the awake relaxed state. Hypnagogic hallucinations were not associated with measurable blood flow changes. The occipital activation supports stage-1 sleep as a state of imagery, while blood flow decreases in premotor cortex, thalamus, and cerebellum suggest reduced preparedness for goal-directed action. Stage-1 sleep appears more similar to altered awareness states like relaxation meditation than to deeper sleep, and may represent the dreaming state of wakefulness, distinct from REM sleep dreaming.