Responding for sucrose and wheel-running reinforcement: Effect of prerunning

Six male albino Wistar rats were placed in running wheels and exposed to a fixed interval 30-s schedule that produced either a drop of 15% sucrose solution or the opportunity to run for 15 s as reinforcing consequences for lever pressing. Each reinforcer type was signaled by a different stimulus. To assess the effect of prerunning, animals were allowed to run for 1 h prior to a session of responding for sucrose and running. Results showed that, after prerunning, response rates in the later segments of the 30-s schedule decreased in the presence of a wheel-running stimulus and increased in the presence of a sucrose stimulus. Wheel-running rates were not affected. Analysis of mean postreinforcement pauses (PRP) broken down by transitions between successive reinforcers revealed that prerunning lengthened pausing in the presence of the stimulus signaling wheel running and shortened pauses in the presence of the stimulus signaling sucrose. No effect was observed on local response rates. Changes in pausing in the presence of stimuli signaling the two reinforcers were consistent with a decrease in the reinforcing efficacy of wheel running and an increase in the reinforcing efficacy of sucrose. Prerunning decreased motivation to respond for running, but increased motivation to work for food.