The development of self-reinforcing running in satiated rats

Fast, “playful” running was obtained in rats never given reward for running in an alley. The maintenance of such running was not dependent on hunger, thirst, or an “exercise” drive produced by confinement in small home cages. However, hunger facilitated the development of “playful” nonrewarded running in rats which initially did not run when food-satiated. “Playful” running was not seen in hungry, rewarded rats or in hungry, nonrewarded rats fed immediately after their daily running sessions. Probably incentive, but not drive, prevents the occurrence of self-reinforcing running.