Secondary extinction reduces reinstatement of threat expectancy and conditioned skin conductance responses in human fear conditioning

Abstract Background and objectives Secondary extinction refers to the phenomenon that extinction of one conditioned stimulus (CS) results in the reduction of conditioned responses for other CSs conditioned with the same unconditioned stimulus (US). Previous research with rats has demonstrated that secondary extinction can interfere with the return of conditioned fear after a reinstatement manipulation. Here we investigated this phenomenon in two pre-registered studies in humans. Method In both experiments, distinct CSs were paired with an electrical stimulation. Next, conditioned reactions to both CSs were extinguished and thereafter reinstated through the administration of three unsignaled electrical stimulations. Crucially, before participants continued with the reinstatement test, half of the participants received secondary extinction trials whereas the other half did not receive these trials. Results Our results indicate that secondary extinction reduced reinstatement of threat expectancies and skin conductance responses, but the effect on skin conductance was only found in the second experiment. Limitations The studies were conducted in a laboratory setting with healthy students. Additional research will be required to determine the feasibility of applying secondary extinction in a (sub)clinical context. Conclusions To our knowledge, this is the first demonstration of secondary extinction and its effect on reinstatement of conditioned fear in humans. We relate our findings to the earlier research with rats and discuss their relevance for exposure therapy.