Learning improvement of appetitively or aversively reinforced light-dark discrimination and reversal four weeks after electrical stimulation of the lateral hypothalamus of the rat.

The experiments reported here point out the effect of electrical stimulation of the lateral hypothalamus on the acquisition and reversal of a simultaneous light-dark discrimination performed 4 weeks later. The stimulation was applied on 15-day-old rats. There were two control groups, implanted but not stimulated and non-implanted rats. In the first experiment, the light-dark discrimination task was food-reinforced. As already reported in the case of an appetitively reinforced operant task, stimulation of the lateral hypothalamus induced an important improvement of performance in discrimination and reversal. This improvement was already apparent at the beginning of acquisition. In the reversal task the mean response latency of stimulated rats was greater than tht of control animals. In the second experiment with naive rats we used the same discrimination but the task was aversively reinforced by an electric foot-shock. In spite of the different type of reinforcement used, the stimulated rats performed better than the control rats in the three behavioral situations studied: avoidance, discrimination and reversal. As in the first experiment the improvement appeared at the onset of acquisition in the three situations. Thus the long-term effect of lateral hypothalamic stimulation does not depend on the type of reinforcement, nor the behavioral task. These results are briefly discussed.