Amygdala neurons mediate acquisition but not maintenance of instrumental avoidance behavior in rabbits

Whereas the amygdala is generally understood to be involved in aversively m otivated learning, the specific associative function of the amygdala remain s controversial. This study addressed the amygdalar role in mediation of di scriminative instrumental avoidance learning of rabbits. Bilateral microinj ection of the GABA receptor agonist muscimol centered in the basolateral nu cleus of the amygdala was given to inactivate amygdalar neurons at each of three stages of acquisition. The absence of behavioral learning in rabbits trained immediately after amygdalar inactivation confirmed previous results with electrolytic lesions. The absence of savings during training after mu scimol had become ineffective indicated an amygdalar role in the establishm ent of acquisition-relevant neural plasticity, not simply in the expression of the learned response. A time-limited role of the amygdala in instrument al avoidance learning was indicated by the finding that intra-amygdalar mus cimol failed to disrupt performance of the well-established avoidance respo nse. The passage of time alone (with no training trials) was sufficient to reduce amygdalar involvement in response performance. These results and dem onstrations that other limbic system areas make time-limited contributions to learning indicate that the amygdala is part of a larger intermediate mem ory system that supports learning and performance before habit consolidatio n.