"Dopamine is released when you're doing something [highly] pleasurable," like having sex, doing drugs or eating chocolate, says Larry J. Young, a psychiatry professor at ... Emory University.
Love and dopamine are not all about young lovers; a bit later, there's stuff for middle-aged (and above) married couples:
... [A] great deal of research shows that doing novel, exciting things together boosts marital happiness. "Take a class together that you know nothing about," suggests Aron, who has co-written several studies in this area. "See a play, go to a new location, go to a horse race." The release of dopamine during these activities might remind couples of how it felt to fall in love or even be happily misattributed to the experience of being together.
Also, says Acevedo, be thoughtful with your partner.
"We know that things like celebrating the positive is important for a relationship's well-being, as well as being supportive when [our partners] need us," she says. Couples that took part in Acevedo's study also resolved conflict smoothly and quickly, were affectionate and communicated openly with their partners, and spent time bettering themselves as well as the relationship.
"And sex!" she adds. "Sex is always good."
While on the topic of married couples, John Medina at Brain Rules has a post on marriage reinvention.