The effects of pretraining on the bar-pressing performance of VMH-lesioned rats

Ventromedial hypothalamic lesioned rats preoperatively trained on an FR-128 schedule displayed postoperative improvements in performance which were a direct function of the degree of hyperphagia. The postoperative performance by the pretrained VMH-lesioned animals did not significantly differ from that of control animals during short test sessions following periods of deprivation, but substantially exceeded that of controls with continuous opportunity to respond. The increase in the number of pellets obtained was achieved by increases in both the meal size and the rate of bar-pressing. Previous attempts to account for the deficit in performance by nonpretrained VMH-lesioned animals in terms of decreased motivation or lowered activity are rejected in favor of an explanation based on a modification of affective response following such lesions.