Response involvement in brain stimulation reward

The hypothesis that responding contributes to the reward value of brain stimulation was tested in two novel experimental paradigms. In the first experiment rats lever-presssed for rewarding brain stimulation during 90 sec periods. After each period the lever automatically retracted and experimenter-administered stimulation (EAS) was presented at the same rate and current parameters as during the self-stimulation (SS). The rats could demonstrate a preference for SS (vs EAS) by pressing a reset lever on the opposite wall of the test chamber. This action terminated the EAS and reinstated the SS-lever for an additional 90 sec. Results showed that the rats preferred to respond for stimulation than to have that same stimulation administered by the experimenter. This was true even when a signal preceded each train of EAS or when subjects had a great deal of previous EAS experience. In the second experiment conditioned taste preferences were observed following novel taste/SS pairings but not following novel taste/EAS pairings. The data from these two experiments suggest that responding contributes to the rewarding value of brain stimulation.