Brain mechanisms underlying experimentally-induced ‘social problem’ in rats

Abstract

Exploitation of workload or labor in groups is a distinctive characteristic of social animals, ranging from worker ants to humans. However, the neurobiology underlying behavioral strategies of individuals’ actions and credits in social settings involving workload imbalance is not well understood. Here we show that the anterior cingulate cortex (ACC) plays a necessary role in the expression of exploited behavior under social competition for resources. A stable ‘worker-parasite’ relationship developed when three individually operant-conditioned rats were placed together in a Skinner box equipped with response lever and food dispenser on opposite sides. Specifically, one rat, the ‘worker,’ engaged in lever-pressing while the other ‘parasitic’ rats profited by crowding the feeder in anticipation. c-Fos expression in the ACC was significantly higher in worker rats than in parasite rats. ACC inactivation suppressed the worker’s lever-press behavior under social, but not individual, settings. Moreover, GABA- and potassium channel-related mRNA expressions decreased in the worker’s ACC. These results suggest that the ACC integrates cost-benefit and social competition information to control effortful behavior. They further suggest putative molecular pathways, namely reduced expressions of GABA-related proteins and potassium channels, that enhance ACC’s neural activity so as to promote effortful behavior in a social dilemma setting.