Conditioning response theory and expectancy theory are primary explanatory models of placebo effect formation within deceptive placebo (DP) paradigm and considered either independent from each...Show moreConditioning response theory and expectancy theory are primary explanatory models of placebo effect formation within deceptive placebo (DP) paradigm and considered either independent from each other (Voudouris, 1990) or related in a form of mediation (Wager, 2005). Additionally, recent development of open-label placebo (OLP) framework has made it possible to apply placebos in clinical practice in a more ethical way while also raising the question as to what enables to observe the placebo effect in this paradigm since the deception is not used. The latter questions the hypothesis of expectancy mediation that holds that placebo occurs when a subject expects it to. Therefore, this study will investigate the role of expectancies in a conditioned placebo response within OLP and DP paradigms. In this study it was hypothesized that 1) conditioning would result in positive placebo effect in both experimental groups, 2) mediating role of expectancies in conditioning shaped placebo effects was hypothesized to be observed when OLP and DP groups scores are combined and 3) mediation of expectancies should be observed in DP group but not in OLP group. To address these hypotheses, an interventional single blinded randomized controlled trial design was used with group differences as between subject factor and activation or deactivation of sham device as within subject factor. Thermal heat pain was used for pain induction. To elicit placebo effects, conditioning procedure together with relevant verbal suggestions about the sham device were delivered. Together, 88 participants were tested with no baseline differences in age, gender, warmth and pain thresholds, and applied temperatures. Conditioning successfully predicted placebo outcome measures. Mediation analysis revealed that expectancies partially mediated conditioning-placebo effect relationship in DP, but not in OLP groups. The findings signify the different mechanisms in DP and OLP framework and points to possible future research directions. Ultimately, full understanding of placebo effects would allow for better treatment of people with chronic conditions, such as chronic pain.Show less
Within placebo research, a discussion has arisen on whether hiding the true nature of this inert treatment is deceptive. Therefore, the administration of an ‘open-label placebo’ (OLP) was...Show moreWithin placebo research, a discussion has arisen on whether hiding the true nature of this inert treatment is deceptive. Therefore, the administration of an ‘open-label placebo’ (OLP) was introduced, a more ethical way to administer the inert treatments by disclosing the intentions of the placebo. Research focusing on the underlying mechanisms of the placebo effect, i.e. the inclusion of classical conditioning, enhancing expectations with verbal suggestions and personality factors such as optimism has yet to focus on the role of these mechanisms in OLP groups. The present study investigated whether there is a difference between OLP and deceptive placebo (DP) effects in experimentally induced heat pain in healthy individuals. Additionally, the role of pain expectations and optimism was studied for both groups. Sixty participants received pain induced by thermal stimuli and were randomized into two groups. For the OLP group, the analgesic placebo device was described as inert and conditioning happened by reducing the stimulus intensity. For the DP group, the placebo device was described as analgesic and conditioning also happened. Pain ratings and expectations were measured verbally throughout the procedure. Optimism was measured with the LOT-R. Placebos were measured by comparing pain for non-placebo and placebo stimuli. Results showed no difference between OLP and DP groups (F(1, 58) = .155, p = .695, ηp2 = .003). Analgesic placebo effects were found for both groups (F(1, 58) = 26.111, p < .005, ηp2 = .310). Expectations significantly predicted the placebo effect in the DP group (β = -.348; t(27) = -5.153, p < .05), and the OLP group, however for which the results needed to be interpreted with caution., This implies that higher pain expectations led to smaller placebo effects. No effect for optimism was found. Results suggest that both OLP and DP groups produce a similar analgesic effect. This finding implies that in future treatments, it could be considered to use OLP versions of placebo treatments as a more ethical and efficient version of the deceptive placebo treatments. Future research could further specify the individual characteristics that could enhance the success of placebo treatments in a more ethical way.Show less
