Effects of bilateral lesions of the central and lateral amygdala on free operant successive discrimination.

Male rats received either ibotenic acid (IBO) or sham lesions bilaterally into the central or lateral amygdala or were assigned to an unoperated control group. After the postoperation recovery period all lesioned and unoperated animals were tested for open field behaviour and for the ability to master a free operant successive discrimination. Retention of the discrimination learning was evaluated 48 h later for the original and reversal problem. After the reversal learning retention test the unoperated animals were assigned at random to one unoperated control and two IBO amygdaloid lesioned groups (central and lateral) and these, unoperated and lesioned animals, received additional free operant successive discrimination retraining after the surgery recovery period. Significant lesion effects were found in the emotional indices in the open field test. The lesions significantly impaired the postoperative acquisition of a free operant successive discrimination and its reversal and diminished its retention but did not impair the retention of such a discrimination task acquired before the lesion. The contribution of central and lateral amygdala in open field behaviour and in the major components of a free operant successive discrimination is discussed. In order to know how the amygdala is involved in association of sensorial stimuli with reinforcement we suggest experimental designs controlling the detailed components of such an association.