glucose
The brain is a marvelous organ. And its a hungry one, too. The major fuel for the brain is the carbohydrate glucose. The average adult brain represents about 2% of our bodys weight, but uses 25% of the glucose in the body. Moreover, specific areas of the brain use glucose at different rates. If you are concentrating hard, taking a test, for example certain parts of the brain need a lot of extra glucose while other parts of the brain only use their normal amount. Something to think about.