Changes in heart rate during suppression of operant responding in pigs

Three groups of four pigs were subjected to a conditioned emotional response (CER), a time-out and a punishment procedure, each involving a discrimination between a positive and a negative conditioned stimulus. In the CER group and in the punishment group, pigs soon learned to suppress responding during the CS+, showing at the same time a marked bradycardia. Pigs in the time-out situation showed no consistent changes in heart rate although a marked decrease occurred in response rate. In all the conditioning procedures a clear discrimination was demonstrated between the CS+ and CS-. The results are interpreted in terms of interference between heart rate and general activity.