Then , after 15 minutes , the brain 's anterior cortical regions receive normal daytime blood flow .
Studies using advanced imaging have shown that cerebral blood flow will return to waking levels in the brainstem and thalamus first .
After 15 minutes , the brain 's anterior cortical regions receive normal daytime blood flow .
Studies using advanced imaging have shown that cerebral blood flow will return to waking levels in the brainstem and thalamus first .