Effects of amygdala lesions on reflex facilitation and conditioned response acquisition during nictitating membrane response conditioning in rabbit.

The present study demonstrated that large lesions of the amygdala disrupt the maintenance of reflex facilitation of the unconditioned nictitating membrane (NM) response and slow the acquisition of conditioned NM responses in rabbit. Before behavioral training, the central nucleus of the amygdala and adjacent areas were lesioned electrolytically. In the 1st experiment, the lesioned animals exhibited no reflex facilitation of the unconditioned NM response at conditioned stimulus (CS)-unconditioned stimulus (US) intervals of 125-8,000 ms. In the 2nd and 3rd experiments in which one CS-US interval (500 ms) was used, the lesions disrupted the maintenance of reflex facilitation but did not alter the facilitation exhibited in the 1st block of training. The lesions retarded the acquisition of conditioned NM responses when the 1000-Hz tone CS intensity was 65 dB but not when the intensity was 85 dB.