Social dominance rank influences wheel running behavior in mice

Dominance hierarchies within social groups determine resource distribution. Resources, such as food and access to mating partners, can act as reinforcers. The present study examined the effect of social rank on access to wheel running-a reinforcing behavior performed by laboratory animals. Mice were identified as dominant or subordinate and given access to a running wheel access under solitary or social conditions. In the solitary condition, subordinate and dominant mice spent equal amounts of time on the running wheel. In the social condition, when one wheel was present, subordinate mice spent less time on the wheel than did dominant mice. Conversely, when two wheels were present, subordinates spent more time on the wheel than did dominant mice. When mice were given 24h access to one running wheel in the social condition, dominant mice ran more than subordinates during the dark cycle. Subordinate mice did not compensate for the lack of running wheel access by schedule shifting. These results suggest that social rank influences access to reinforcers by behavioral interference rather than by social inhibition.