Via Dr. Helen Fisher:
"My hypothesis? Foremost, I suspected I would find elevated activity in the brain’s networks for dopamine, a natural stimulant—because this brain system generates energy, euphoria, craving, focus, and motivation, some of the core traits of romantic love. I also posited that the closely related neurochemical norepinephrine might contribute to this madness, because this neurotransmitter produces focus and motivation too, as well as some of the bodily responses of romantic love such as butterflies in the stomach, wobbly knees, and a dry mouth. And I thought low activity in the serotonin system might create the intrusive, obsessive thinking of romantic passion. Last, I expected that many other neurochemical systems might be involved—together producing the range of emotions, motivations, cognitions, and behaviors common to romantic love. But my bets were on dopamine."