Effect of disruption on wheel-running reinforcement on rates of wheel running and operant lever pressing in rats

Abstract

The current study investigated the effects of interruptions in wheel running on operant responding for a fixed bout of wheel-running reinforcement. Interruptions in the fixed bout of reinforcement occurred after rats completed different numbers of wheel revolutions and were designed to vary the local constraint on wheel running, while holding constant the total number of revolutions per session, the overall constraint. Eleven female Long-Evans rats responded on response-initiated variable interval 15-s schedules for the opportunity to run for 30 revolutions, with a 4.5-s wheel-brake asserted after 2, 5, 10 or 15 revolutions. After the brake disruption, rats had to complete the remainder of the 30-wheel turns required for the bout of wheel-running reinforcement. Results showed that wheel-running rates and overall lever-pressing rates followed a bitonic, inverted-U function for wheel revolutions completed before the 4.5-s interruption. These results suggest that interruptions of wheel-running within a reinforcement opportunity systematically altered wheel-running rates and lever-pressing rates. Notably, similar effects have been obtained when local constraint is manipulated as the number of wheel revolutions per reinforcement. Interruptions of wheel running within fixed bouts of wheel-running reinforcement, however, produced weaker effects than local constraint based on the number of revolutions per reinforcement, likely due to the wheel revolutions after the disruption which were required to complete each reinforcement. In sum, these results support an account based on local constraint on an automatically reinforced behavior rather than reinforcement magnitude to explain how wheel-running and lever-pressing rates change with revolutions per reinforcement.