The undermining effect of sucrose reinforcement on automatically-reinforced operant wheel-running study in rats

Abstract

The undermining effect can be defined as a decrease in levels of intrinsic motivation for a behaviour as a consequence of the delivery and subsequent removal of a contingent extrinsically-motivating reward. A well-documented phenomenon in humans, the present study investigated the potential presence of an undermining effect of extrinsic sucrose reinforcement on intrinsically motivated (automatically-reinforced) operant wheel running in eight female Long-Evans rats. In each session, rats ran for 20 min prior to and following operant wheel running on a fixed interval (FI) 60-s schedule. Across three conditions, water, sucrose, and water were delivered as outcomes for operant wheel running on the FI 60-s schedule. No undermining effect was observed for wheel running on the FI 60-s schedule following the removal of sucrose; nor was there a decrease in running during the 20-min post-operant running period. However, wheel running during the 20 min period prior to operant running significantly decreased. Contrary to previous findings, this result suggests that an undermining effect can occur in rats. Explanations for the presence of this effect as well as suggestions for future research investigating this effect in non-human species are discussed.