Intracellular ATP Levels (IMAGE) Tokyo Metropolitan Institute of Medical Science Caption Intracellular ATP levels reflect the balance between energy synthesis and consuming activities in the brain. During REM sleep, brain energy synthesis activities (measured as cerebral blood flow) increased while neuronal ATP levels significantly decreased, suggesting a great increase in neuronal energy-consuming activities. Credit TMIMS Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.