Intimacy is its own source of dopamine. Oxytocin, a hormone much involved with falling in love, mother-child bonding, and lifetime pair bonding of sexual mates, binds to receptors on the dopamine-secreting neurons in the brain’s reward pathway and enhances the firing of the reward-circuit tract. In other words, oxytocin leads to an increase in brain dopamine, a recent finding by Stanford neuroscientists Lin Hung, Rob Malenka, and their colleagues.

