Cerebral oxygen metabolism and cerebral blood flow in man during light sleep (stage 2)

Abstract We measured cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO 2 ) during light sleep (stage 2) in 8 young healthy volunteers using the Kety-Schmidt technique with 133 Xe as the inert gas. Measurements were performed during wakefulness and light sleep as verified by standard polysomnography. Unlike our previous study in man showing a highly significant 25% decreased in CMRO 2 during sleep sleep (stage 3–4) we found a modest but statistically significant decrease of 5% in CMRO 2 during stage 2 sleep. Deep and light sleep are both characterized by an almost complete lack of mental activity. They differ in respect of arousal threshold as a stronger stimulus is required to awaken a subject from deep sleep as compared to light sleep. Our results suggest that during non-rapid eye movement sleep cerebral metabolism and thereby cerebral synaptic activity is correlated to cerebral readiness rather than to mental activity.