Cortex-wide variation of neuronal cellular energy levels depending on the sleep-wake states

The brain is assumed to exert homeostatic functions to always keep the cellular energy status constant, this has not been proven. Researchers discovered that cortical neuronal intracellular concentrations of ATP, the major cellular energy metabolite, greatly decreased during REM sleep, despite a simultaneous increase in cerebral hemodynamics for energy supply, compared with waking in mice. These indicate that cerebral energy metabolism may not always meet neuronal energy demands. Source