Fear extinction is not permanent but is instead more vulnerable than the original fear memory, as traditionally shown by the return of fear phenomena. Because of this, techniques to mitigate the return of fear are needed in the clinical treatment of related psychological conditions. One promising strategy is the occasional reinforced extinction treatment, introducing a gradual and sparse number of conditioned stimulus–unconditioned stimulus (CS-US) pairings within the extinction treatment. We present the results of three experiments in which we used a threat conditioning procedure in humans. Our main aim was to evaluate whether occasional reinforced extinction could reduce two different forms of relapse: spontaneous recovery (Experiments 1 and 2) and reinstatement (Experiment 3). Contrary to our predictions and previous literature, the results indicate that an occasional reinforcement treatment did not mitigate relapse compared with standard extinction. From a theoretical standpoint, these results are more consistent with the idea that extinction entails the acquisition of new knowledge than with the idea that there are conditions in which extinction leads to a weakening of the original fear memory. These findings also question the generality of the potential benefits of using occasional reinforced extinction in clinical settings.
