This is the culprit behind many an all-night poetry fit. This is the reason lovers fight armies, swim oceans, or walk hundreds of miles to be together. In a word, they’re high. Imaging studies confirm new lovers have high amounts of activity in the ventral tegmental area and nucleus accumbens, the same reward systems that fire off in response to inhaling a line of cocaine. These regions are flooded with the neurotransmitter dopamine, a chemical that drives us toward a perceived reward. Other chemicals related to stress and excitement are elevated as well, such as cortisol, phenylephrine (found in chocolate), and norepinephrine. A neurotransmitter called serotonin is low in early romantic love. Serotonin can also be low in obsessive-compulsive disorder, depression, and anxiety. The result is an obsessive pursuit of the desired, a relentless optimism, and even a kind of addiction.