Excitation and inhibition as a function of posttraining extinction of the excitatory cue used in Pavlovian inhibition training

Water-deprived rats served in a conditioned lick-suppression paradigm designed to assess the associative structure underlying a partially reinforced Pavlovian inhibitor. In all experiments, a Pavlovian conditioned inhibition procedure was used in which Stimulus A was consistently reinforced with footshock, and a simultaneous compound of Stimuli A and X was partially reinforced (25%) with footshock (i.e., A+ AX±). Experiments 1 and 2 demonstrated that Stimulus X passed an inhibitory summation test and that postraining extinction of Stimulus A decreased this summative effect. Experiment 3 indicated that Stimulus X passed a retardation test for inhibition and that posttraining extinction of Stimulus A decreased the observed retardation. Experiment 4 provided evidence that posttraining extinction of Stimulus A increased responding to Stimulus X on a direct test for excitation. Thus, extinction of Stimulus A was found to decrease Stimulus X's response potential on retardation and summation tests for inhibition and to increase Stimulus X's response potential on a test for excitation. These observations suggest that the associative response potentials of a stimulus are not solely functions of the associative strength of that stimulus. After partially reinforced Pavlovian inhibition training, Stimulus X and Stimulus A appear to have an inverse relationship in influencing associative responding to Stimulus X regardless of whether responding is measured with tests for inhibition or excitation.