Reinforcement omission, non-contingent reinforcement, and limbic lesions in rats

Abstract

Two groups of six albino rats were given lesions of the septum and dorsal hippocampus respectively. Under an FI 1 min schedule of food reinforcement, septal rats lever pressed at significantly higher response rates than intact controls. Under a modified FI 1 min schedule during which food pellets were occasionally omitted, every subject made more responses in intervals following omissions than in those following pellet deliveries, but rats with hippocampal lesions showed a larger increase in response rate than either controls or septals, which did not differ. In Experiment 2, half of these subjects were subjected to experimental extinction, and half provided with noncontingent reinforcement at 1 min intervals. Both procedures decreased responding, but only under extinction did the experimental groups show slower decreases than the controls. Although these data provide a clear double dissociation for septal and dorsal hippocampal lesions, they present substantial difficulties for both “disinhibition” and “perseveration” theories of septal and hippocampal function.