The role of expectations and endogenous opioids in mindfulness-based relief of experimentally-induced acute pain.

OBJECTIVE Expectations contribute to cognitive pain modulation through opioidergically-mediated descending inhibition. Mindfulness meditation reduces pain independent of endogenous opioids, engaging unique corticothalamo-cortical mechanisms. However, it remains unknown whether expectations for pain-relief predict mindfulness-induced analgesia and if these expectations are modified by endogenous opioids. METHODS In this secondary analysis of previously published work, 78 pain-free participants (mean age 27 ± 7 years; 50% women) were randomized to a 4-session mindfulness meditation or book-listening regimen. Expectations for intervention-induced pain-relief were assessed before and after each intervention. Pain ratings were examined after meditation or rest (control group) during noxious heat (49°C) and intravenous administration of saline-placebo or the opioid antagonist naloxone (0.15 mg/kg bolus + 0.1 mg/kg/h infusion. RESULTS Mindfulness significantly lowered pain during saline and naloxone infusion. Higher expected pain-relief from mindfulness predicted lower pain intensity, r(40) = -.41, p = 0.009. The relationship between meditation-related expectations and pain intensity reductions were exhibited during naloxone, r(20) = -.76, p < .001 but not saline, r(20) = -.22, p = 0.36. Expectations for book-listening based analgesia did not significantly predict pain changes during saline, r(20) = -.37, p = .11 or naloxone, r(18) = 0.26, p = .30 in the control group. CONCLUSIONS These novel findings demonstrate a significant role for expectations in mindfulness-based pain-relief. However, this role was minimal during saline and stronger during opioid blockade, despite similar pain reductions. This supports growing evidence that mindfulness engages multiple mechanisms to reduce pain, suggesting that mindfulness might be an effective pain-reducing technique even for individuals with low expectations for pain-relief.