Post-trial stimulation and the acquisition of conditioned suppression in the rat

Three experiments investigated the effect of post-trial stimulation on conditioning. Rats were trained in a conditioned suppression procedure in which only half of the CS presentations were followed immediately by a shock reinforcer. Presenting a second, post-trial, shock 8 s after the end of reinforced CS presentations increased resistance to extinction in Experiment I and facilitated conditioning in Experiment II relative to a condition in which the same post-trial shock was delivered 8 s after non-reinforced trials. Experiment III demonstrated that prior exposure to pairings of the shock reinforcer and the post-trial shock also enhanced subsequent conditioning, and thus ruled out an explanation of the facilitation in terms of the surprising nature of the post-trial stimulation.