In this journal, Vyazovskiy et al. reported deoxyglucose data that they interpreted as supporting the Tononi and Cirelli hypothesis that cerebral metabolic rate (CMR) increases across waking. We summarize contradictory PET-deoxyglucose data that show CMR is the same in the morning and evening and that it decreases rather than increases after a night of sleep deprivation. We propose an alternative model of CMR-sleep homeostasis relations that points to novel experiments.