The prediction of the analgesic placebo effect is moderated by direction of attention: Results from fibromyalgia and healthy controls

Despite extensive research, reliable predictors of the placebo response remain elusive. The within-subject variability (WSV) of pain reports has emerged as a potential predictor, with multiple studies confirming its predictive value. But the results have been mixed. We recently showed that direction of attention moderates WSV's role in predicting the placebo response in patients with chronic back pain. This observational study aims to further examine the relationship between direction of attention, WSV, and the placebo effect in fibromyalgia patients (FM) and healthy controls. Participants completed a demographic questionnaire, clinical pain diaries (for FM), and the revised Self-Consciousness Scale (SCS-R). Afterward, participants underwent two experimental procedures: (1) the Focused Analgesia Selection Test (FAST), assessing experimental WSV of pain reports, and (2) an experimental placebo paradigm. Moderation and regression analyses examined the role of the SCS-R subscales in moderating the prediction of the placebo effect by the WSV of pain reports. Sixty-nine participants (healthy: 37, FM: 32) completed the protocol. Groups did not differ in SCS-R subscales, WSV, or placebo effect magnitude (p≥0.281). At low levels of private self-consciousness (p=0.013) and social anxiety (p=0.017) among FM, clinical WSV played a significant role in predicting the placebo effect. Public self-consciousness for FM showed a similar trend toward significance. These findings underscore attention as a relevant moderator of the placebo effect, emphasizing the need for improved measurement tools to predict the placebo effect. PERSPECTIVE: We highlight the role of direction of attention in the prediction of the placebo effect. Our current findings validate our previous recent results from a cohort of chronic back pain patients, implying that direction of attention should be used in future attempts to improve the prediction of the placebo effect.