Temporally Specific Extinction of Pavlovian Conditioned Inhibition

Abstract

In Pavlovian conditioned inhibition, conditioned stimulus A (CS A) is trained to predict the occurrence of an unconditioned stimulus (US), but when CS A is presented in compound with CS C, the US is omitted. Thus, CS C comes to predict the omission of the otherwise expected US; That is, CS C becomes a conditioned inhibitor. A Pavlovian conditioned inhibition procedure (i.e., A-US / AC-no US) was used in two experiments to test whether conditioned inhibition to CS C is dependent upon the excitatory value of its training excitor (CS A), and whether this inhibition is specific to the temporal location of the excitatory response potential of the training excitor. CS A was made excitatory in two separate temporal locations; its initial and final segments. In Experiment 1, the excitatory potential of the initial segment of CS A was extinguished while the final segment remained unchanged. In Experiment 2, the excitatory potential of the final segment of CS A was extinguished while the initial segment remained unchanged. In both experiments, a retardation of acquisition training phase was used to determine whether manipulating the excitatory potential of training excitor, A, altered the inhibitory potential of conditioned inhibitor, C. CS C proved to be inhibitory in the segment paired with the segment of CS A that remained excitatory, but was abolished in the segment that was paired with the segment of CS A that received extinction. Thus the present results indicate that conditioned inhibition is dependent upon the excitatory potential of a training excitor and that this inhibition is temporally specific.