The early stages of a romantic relationship spark activity in dopamine-rich brain regions associated with motivation and reward. The more intense the relationship is, the greater the activity.

The regions associated with emotion, such as the insular cortex and parts of the anterior cingulate cortex, are not activated until the more mature phases of a relationship, says Helen Fisher, an anthropologist from Rutgers University in New Jersey.

Fisher and colleagues recruited seven male and 10 female volunteers who claimed to be madly in love. They asked them to look at pictures of either their loved one or another familiar person while inside a functional MRI scanner.

Eating chocolate

Early on in a relationship, the images showed that the brain seems to be very focused on planning and pursuit of pleasurable reward, says Fisher, mediated by regions called the right caudate nucleus and right ventral tegmentum. The same regions become active when a person enjoys the pleasure of eating chocolate, she adds...