If you know a little about the human brain, you know it is run by chemicals. To be more specific, our brain is run by serotonin and dopamine, which can make us happy or sad, awake or sleepy, and testosterone and estrogen, which can make us aggressive or peaceful. Indeed we are much more ruled by chemicals than we'd like to think. Which of these crucial 4 chemicals is working overtime in YOUR brain? Complete our quiz to find out.