Neurocognitive Mechanisms of Pain Relief

Background: Chronic pain affects approximately 3.2 million Australians (one in five) every year, and is currently Australia’s third most costly health care problem, resulting in economic costs estimated at over $34 billion per annum.\ua0 Two widely applied treatments for pain are mindfulness meditation and hypnosis, although the mechanisms underlying their beneficial effects are poorly understood. \ua0Theoretically, mindfulness-meditation may be conceptualized as an attentional bias modification paradigm as it trains individuals to non-judgmentally (i.e., without bias) hold attention in the present moment.\ua0 Advancing theory in relation to these two interventions requires a better understanding of the unique mechanisms (i.e., how these treatments work) underpinning these treatments, as well as the moderators of response (i.e., for whom do these treatments work).\ua0 It was hypothesised that a potential mediator of mindfulness-meditation is reduced attentional bias to pain (i.e., hypervigilance). \ua0On the other hand, hypnosis involves an induction procedure followed by suggestions that target changes in how specific elements of the presenting problem are processed, such as a suggestion to shift beliefs from pain as a threat to pain as a non-threatening sensation. \ua0Thus, change in threat appraisals was hypothesised to be a mediator of hypnosis.Methods: 201 healthy adult undergraduate students and their community networks were randomly assigned to one of three conditions: (1) mindfulness meditation, (2) hypnosis, or (3) an attention control.\ua0 Exclusion criteria included diagnosed medical conditions (including chronic pain) and current psychiatric treatment.\ua0 The sample was mostly female (74%), Caucasian (58%), with a mean age of 24-years.\ua0 Participants were assessed on the mediators (dot probe; Pain Appraisal Inventory [PAI]-Threat scale), moderators (sleep, memory, attention, concentration, modified Stroop), and experimental pain outcomes as assessed in relation to the cold pressor task (peak pain intensity; unpleasantness, threshold, tolerance). \ua0Participants were randomised to condition (single-session) then completed these assessments again. \ua0Preacher and Hayes PROCESS bootstrap mediation models and Omnibus Groups Regions of Significance (OGRS) moderation models were used to test the hypotheses. \ua0Bivariate Pearson correlations were used to examine the associations of threat appraisal and attentional bias processes on pain outcomes. Results: Correlations showed threat appraisals and catastrophic thinking styles where negatively associated with pain tolerance and threshold, while attentional domains (e.g., attention, concentration), non-judgment, non-reacting, and resilience were positively associated with pain tolerance; non-reacting and resilience were positively associated with pain threshold.\ua0 In the PROCESS mediation models, both mindfulness meditation and hypnosis reduced pain intensity, while hypnosis reduced pain unpleasantness.\ua0 Changes in threat appraisals specifically mediated outcome in the hypnosis condition, with reduced threat appraisals underlying improved pain tolerance.\ua0 Moderation analysis indicated that higher baseline levels of cognitive flexibility/concentration were associated with increased pain intensity across all conditions; and lower baseline cognitive flexibility/concentration interacted negatively with hypnosis.\ua0 Higher baseline levels of hypervigilance and/or attentional bias towards negative emotion words resulted in worse pain threshold (hypnosis treatment group).\ua0Conclusions:\ua0 Both mindfulness meditation and hypnosis were efficacious in reducing pain intensity, and hypnosis also led to improved unpleasantness. Reduced threat appraisals were found to partially mediate the impact of hypnosis on pain intensity and unpleasantness.\ua0 However, none of the mediators tested were found to underlie the observed improvements with mindfulness meditation. \ua0The moderation findings did however suggest that different individuals might be more or less suitable to mindfulness meditation versus hypnosis. Additional research to identify the mechanisms underlying the beneficial effects of evidence-based psychosocial treatments is required so that they can be streamlined and optimised. \ua0Keywords: chronic pain, experimental pain, mindfulness meditation, hypnosis, moderation, mediatio