It's a given that the brain uses more energy than any other human organ but what does it use that energy to do? A study at the University of Minnesota Medical School has identified where the bulk of that energy goes. Wei Chen, radiologist and co-author of an article entitled "Why Does the Brain need So Much Power?" used MRS (Magnetic resonance spectroscopy) to track the rate of adenosine triphosphate (ATP) production in rat brains, which is the primarily source of cellular energy. The study found that two thirds of the brain's energy budget is used to help neurons "fire" or send signals. The remaining third is used for brain "housekeeping" activities or cell-health maintenance. The team also used MRS to study energy demands of a cat's brain. Next up? Humans, which Chen says they hope to study very soon..