The first comprehensive view of how social interactions can activate the reward systems in the brain that drive monogamous bonding is published online this week in Nature. Observations made in prairie voles, one of the few socially monogamous mammals, may help us to understand how specific patterns of brain activity can contribute to bond formation between two individuals.
Adult pair-bonding involves several notable changes in the perception and valuation of another individual. One key change happens when potential partners begin to reliably activate the brain’s reward system in each other, although the precise neural mechanisms by which such rewarding leads to bonding remain unclear.
Robert Liu and colleagues used the social bonding model of the prairie vole to study the corticostriatal circuit in the brain, which is known to control the ability of animals to alter their behaviour to obtain rewards. The authors recorded the activity of this circuit in female voles during six-hour cohabitation periods with male voles, and found that the strength of corticostriatal connectivity predicts how quickly the animals begin to bond, which is expressed through mating and side-by-side huddling. By rhythmically activating this circuit using an optogenetic (light-mediated) technique in a social context without mating, the authors were able to influence the females’ later preference for partners over strangers. The findings suggest that activity of this circuit not only correlates with bonding behaviour, but also may accelerate it. However, the authors acknowledge that further testing of their hypothesis is required to determine whether this circuit is not just sufficient but necessary for increasing bonding behaviour in these animals.