Dynamic features of hemodynamic and metabolic changes in the human brain during all-night sleep as revealed by near-infrared spectroscopy.

By the use of near-infrared spectroscopy, hemodynamic and metabolic changes were monitored continuously in the human brain during all-night sleep in a similar time dimension as closely monitored by electroencephalography. Measurements were started in the awake state, the values of which were taken as the control. Contrary to what many have predicted, the cerebral oxygen metabolic rate (CMRO2) increased during the transition from wakefulness to sleep. Cerebral blood flow (CBF) decreased during non-rapid eye movement (non-REM) sleep, in which a dissociation between changes in CBF and those in CMRO2 was observed. The CBF returned to the control level even in response to the only 20-s appearance of alpha activity on the electroencephalogram. During REM sleep both CBF and CMRO2 were practically the same as the control level, whereas during the transition from REM sleep to arousal a disproportionate increase in CBF compared with CMRO2 was observed. Thus, it is suggested that the flow-metabolic coupling mechanism is reset to a new level during sleep.