INVOLVEMENT OF THE CENTRAL NUCLEUS AND BASOLATERAL COMPLEX OF THE AMYGDALA IN FEAR CONDITIONING MEASURED WITH FEAR-POTENTIATED STARTLE IN RATS TRAINED CONCURRENTLY WITH AUDITORY AND VISUAL CONDITIONED-STIMULI

The goal of this work was to test the involvement of the central nucle us and basolateral complex of the amygdala in fear conditioning, using auditory and visual conditioned stimuli (CSs). The acoustic startle r eflex in rats was used as the behavioral index of conditioning because startle is reliably enhanced in the presence of a conditioned stimulu s (CS) previously paired with a footshock. Initially, differential con ditioning procedures indicated reliable discrimination between a noise CS and a visual CS. Subsequently, the effects of amygdala lesions wer e evaluated when both modalities were paired with shocks in the same r ats. Electrolytic or ibotenic acid lesions of the central nucleus of t he amygdala blocked fear-potentiated startle to both auditory and visu al CSs, consistent with the idea that the central nucleus serves as a response independent, final common relay for fear conditioning. Simila rly, pre- or posttraining electrolytic or NMDA-induced lesions of the basolateral complex of the amygdala, which damaged the lateral nucleus , and most of the basolateral nucleus, disrupted fear-potentiated star tle to both CS modalities. This finding is consistent with the suggest ion that, in fear conditioning, the basolateral complex of the amygdal a serves as an obligatory relay of sensory information from subcortica l and cortical sensory areas to the central nucleus of the amygdala.