INFLUENCE OF VENTRAL MESENCEPHALIC LESIONS ON VARIOUS SPONTANEOUS AND CONDITIONED BEHAVIORS IN RAT

In the first set of experiments, we used groups of rats with either bilateral or unilateral ventral mesencephalic lesions and a group of controls in the following tests: diurnal exploratory activity, nocturnal activity, Skinner box and avoidance conditioning. Both groups of lesioned rats were found to be hyperactive in both types of activity tests, but those with unilateral lesions showed hyperactivity to a lesser extent. Neither of the experimental groups showed any evidence of extinction in the Skinner box. Rats with bilateral lesions learn a conditioned avoidance response more easily than the control animals but they also tend to show inadaptive behavior during the course of the testing procedure. In a second experiment, stimulating and recording electrodes were implanted in the lateral hypothalamus in certain of the animals of the three previous groups, having lesions as well. Such lesions were found to significantly decrease the threshold of arousal to central hypothalamic stimulation. From the results of our lesioning and testing procedures, a syndrome has been defined. However, the complex structure of the region that was destroyed does not permit a clear interpretation of the results. © 1969.