Project Summary/Abstract Almost one fifth of the adult population in the United States is afflicted with fear-related disorders, including diagnoses such as generalized anxiety disorder, phobias, and PTSD. Yet, despite significant advances in research regarding fear reduction, treatments for these disorders are only moderately effective. Therefore, building our understanding of how to reduce harmful fears is of paramount importance. One step in this process is to further explore the safety signal category. Current views hold that all safety signals are harmful in the context of fear reduction, such that their presence prevents fear extinction from occurring. However, recent findings indicate that certain safety signals?social support figures?may enhance, not prevent, fear extinction. Thus, the proposed research seeks to investigate the as-yet unexplored mechanism by which social support has the unique ability to enhance fear extinction, paving the way for future research investigating whether social support can enhance treatment outcomes for fear-related disorders. Given the important role of the opioid system in both supporting the negative feedback model of fear learning and reinforcing and maintaining social relationships, it is possible that by triggering the release of endogenous opioids, social support disrupts the typical function of the neurobiological associative circuit that that regulates fear learning. This associative circuit relies on opioid processes for fear extinction to occur, such that if opioid processes are blocked, fear extinction is prevented, or if opioid processes are augmented by the presence of a concurrent excitor (an additional fearful stimulus which increases fear and consequent opioid release), fear extinction is enhanced. Thus, unlike learned safety signals, which inhibit opioid processes and prevent fear extinction, social support stimuli might have the unique effect of increasing opioid release without increasing fear, ultimately enhancing fear extinction. This work will seek to more closely examine this mechanism by 1) distinguishing social support stimuli from typical, learned safety signals and determining whether social support stimuli perform the same functions as concurrent excitors but without increasing fear and 2) examining whether opioid processes underlie these effects. In the first study, we will examine whether healthy, adult participants (n=30, 15 females) undergo greater fear extinction when extinction procedures are conducted in the presence of social support stimuli or concurrent excitors compared to in the presence of learned safety signals. In the second study, we will examine whether these effects are still present in healthy, adult participants who are administered placebo (n=30, 15 females) vs. naltrexone (an opioid antagonist known to cross the blood brain barrier and block central opioid processes; n=30, 15 females). Together, the proposed studies will illuminate the mechanism whereby social support enhances fear extinction and may have the potential to shed light on simple, inexpensive ways to enhance current treatments for fear-related disorders.