THE HIPPOCAMPUS AND REWARD - EFFECTS OF HIPPOCAMPAL-LESIONS ON PROGRESSIVE-RATIO RESPONDING

Two experiments investigated the effects of ibotenic-acid lesions of t he hippocampus on food-rewarded performance under a progressive-ratio IO schedule of reinforcement. The results of Experiment 1 indicated th at rats with hippocampal lesions showed profound increases in breakpoi nt and enhancements in the efficiency of responding. In a second exper iment the same rats were challenged with prefeeding, increases in the height of the response lever, and the substitution of sucrose- for gra in-based reward pellets. Responding in both groups was similarly reduc ed by prefeeding and increases in the effortfulness of responding, but lesioned rats were significantly more responsive to the change to suc rose reward. Overall, the results indicated that hippocampal damage in creased responding by enhancing the activational or hedonic properties of the delivered food pellets, while not affecting food-motivation or the motor capacity to respond.