Functional significance of different amygdalar areas in performance of instrumental conditioned alimentary reflexes in rats.

Bilateral lesions of the basolateral amygdala caused facilitation of instrumental alimentary conditioned reflexes while bilateral cortico-medial amygdala damage produced inhibition of conditioned responses. The most rapid learning was in rats after basolateral lesions whereas the cortico-medial rats required more trials to criterion than controls. In basolateral rats the largest number of intertrial responses were found, while cortico-medial rats had a small number of ITR in criterion sessions. Thus, the cortico-medial amygdala was concerned with the excitatory system and the basolateral amygdala with the inhibitory system of the rat forebrain. The results of combined unilateral lesions of basolateral and cortico-medial amygdala in each hemisphere suggest that in healthy animals the inhibitory influence of the former was stronger and overlapped or regulated the excitatory action of the latter. Our evidence suggests the existence of two antagonistic systems in the rat amygdala which play different roles in conditioning.