THE EFFECT OF A CHANGE IN BODY-WEIGHT ON RUNNING AND RESPONDING REINFORCED BY THE OPPORTUNITY TO RUN

Previous research has shown that running increases as body weight decr eases. One interpretation of this relationship is that motivation to r un increases as body weight decreases. In the present study, the relat ionships among body weight, running, and responding for the opportunit y to run were investigated. Fourteen male Wistar rats were trained to respond on levers. The reinforcing consequence was the opportunity to run for 60 seconds. in each session, subjects were exposed to a series of variable-interval schedules. Over sessions, body weight was increa sed from 80% to 100% of an initial ad-rib level and then returned to 8 0%. Results showed that running and lever-pressing rates were lower at the higher body weight whereas mean latency to respond following rein forcement was higher at the higher body weight. Analysis of between su bjects data also revealed orderly relationships. At each body weight, lever-pressing rates were positively related to running rates. In addi tion, changes in running caused by change in body weight were positive ly related to changes in lever-pressing rates and negatively related t o changes in latency Finally, changes in running were not related to i nitial levels of running. In sum, the results were consistent with the interpretation that motivation to run varies with body weight.