Stimulus intensity effects of acute extinction of the CER in rats.

Two groups of 9 rats were trained in the conditioned emotional response (CER) consisting of suppression of food-motivated behavior as a consequence of the pairing of white noise with unavoidable shock. One group was trained and then extinguished with an 80 dB white noise value and the other with the 50 dB white noise intensity as the conditioned stimulus (CS). The CER acquisition was faster with the more intense CS, however, on the last training day, conditioned suppression reached the same asymptotic level in both groups. Then an acute extinction procedure was introduced, wherein the CS was presented only once a day and lasted continuously until the end of the session with no US presentation during this period. This procedure was repeated over several consecutive days. During the first prolonged CS action, CER extinction was more rapid in the 50- than in 80-dB group. However, on the next extinction day the amount of suppression was less with the more intense CS. The results were discussed in terms of CS intensity effects on learning and performance of the conditioned response.