Instrumental lever pressing for wheel running is a bitonic function of wheel revolutions per reinforcement: Effects of constraint and automatic reinforcement

Abstract

The current study investigated the relationship between wheel-running reinforcement and operant lever pressing when an opportunity to run is defined by the number of wheel revolutions rather than duration of wheel access. Twelve female Long-Evans rats responded on response-initiated variable interval 15-s schedules for the opportunity to run for 1, 3, 5, 10, 20, 30, or 40 revolutions. Half the rats received an ascending order of revolutions/reinforcement; the other half, received a descending order. Results showed that wheel-running and lever-pressing rates were described by a bitonic relationship with revolutions/reinforcement, initially rising then falling, as revolutions/reinforcement increased. Long postreinforcement pause (PRP) durations occurred with few revolutions, short PRPs with an intermediate number, and long PRPs again with a high number of revolutions; thus, PRP showed an inverted U-shaped function. Rather than a reinforcement-magnitude interpretation, our findings suggest that number of revolutions/reinforcement (or duration of wheel access) be conceptualized as constraint on an automatically-reinforcing behavior (wheel running). Specifically, we propose that the automatic-reinforcement value of contingent wheel running varies with its rate of occurrence, which causes instrumental lever-pressing rates to vary with wheel-running rates. The current analysis of constraint and the automatic reinforcement of the contingent behavior is shown to further extend the response-deprivation hypothesis to wheel-running reinforcement.