Placebos have been shown to affect both subjective experiences and physiological markers. However, their influence on defensive responses to threat has yet to be investigated. This study examines...Show morePlacebos have been shown to affect both subjective experiences and physiological markers. However, their influence on defensive responses to threat has yet to be investigated. This study examines whether a placebo manipulation can impact subjective pain ratings in response to the shock, as well as heart rate during shock anticipation, in healthy individuals. Participants (n=72) were tested in a Pavlovian threat conditioning paradigm over two days with a 24-hour interval, in a within-subject design. A sham analgesic electrical stimulation (TENS) was used to induce a placebo effect. The placebo conditioning process paired a placebo stimulus ("painful shock + TENS") with a low pain response, followed by two sessions of associative threat conditioning. Subjective pain ratings and heart rate, as an indicator of the freezing response, were measured across different conditions. The STAI-trait questionnaire was also completed. Results indicated higher subjective pain levels in response to the painful shock compared to the TENS shock during the threat acquisition phase. Importantly, during this phase, stronger heart rate deceleration, indicative of freezing, was observed when anticipating the painful shock versus the TENS shock. There was no evidence the placebo effect persisted during the threat retention stage, as there were no significant differences in heart rate while anticipating the two conditions. Trait anxiety did not significantly influence the placebo response. These findings demonstrate that a placebo intervention affects not only subjective experiences but also physiological responses to threat, highlighting the potential of using placebos as co-interventions for individuals experiencing anxiety.Show less
