Did you know that energy levels in the brain change depending on the type of sleep one is experiencing? Reports of rat studies, published in the Journal of Neuroscience, showed that in the initial stages of sleep, energy levels increase dramatically in brain regions that are found to be active during waking hours. Adenosine triphosphate (ATP), the energy currency of cells, was found to surge during non-REM sleep. This surge of cellular energy is thought to replenish brain processes needed to function normally while awake. Sleep appears to be necessary for this energy surge to occur. How well you think while you are awake may be related to whether or not your brain received enough sleep to experience this energy surge of ATP.