AMYGDALAR LESIONS BLOCK DISCRIMINATIVE AVOIDANCE-LEARNING AND CINGULOTHALAMIC TRAINING-INDUCED NEURONAL PLASTICITY IN RABBITS

Learning to fear dangerous situations requires the participation of ne urons of the amygdala. Here it is shown that amygdalar neurons are als o involved in learning to avoid dangerous situations. Amygdalar lesion s severely impaired the aquisition of acoustically cued, discriminativ e instrumental avoidance behavior of rabbits. In addition, the develop ment of anterior cingulate cortical and medial dorsal thalamic trainin g-induced neuronal plasticity in the early stages of behavioral acquis ition was blocked in rabbits with lesions. The development of training -induced neuronal plasticity in the medial dorsal and anterior thalami c nuclei in late stages of behavioral acquisition was also blocked in rabbits with lesions. These results indicate that the integrity of the amygdala is essential for the establishment of both early and late tr aining-induced cingulothalamic neuronal plasticity. It is hypothesized that amygdalar training-induced neuronal plasticity in the initial tr ials of conditioning represents a substrate of learned fear, essential for the early and late cingulothalamic plasticity that is involved in mediation of acquisition of the instrumental avoidance response.