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Papers of the Week

Papers: 21 Oct 2023 - 27 Oct 2023

2023 Oct 21

J Pain


Placebo hypoalgesia and nocebo hyperalgesia induced by observational learning may be difficult to disentangle in a laboratory setting.


Meeuwis SH, Kłosowska J, Bajcar EA, Wasylewski MT, Badzińska J, Rubanets D, Di Nardo M, Mazzoni G, Bąbel P


Observational learning (seeing pain/pain treatment in others) can evoke placebo hypoalgesia and nocebo hyperalgesia. Data that compares these effects and illuminates the role of expectations and empathy is scarce. Healthy participants (n=105) were randomised to: 1) placebo OBL, 2) nocebo OBL, or 3) no-observation control group. Observational learning consisted of a model simulating pain relief or increase after a sham ointment was applied to one arm. Pain was evoked with thermal stimuli on both arms (ointment, contralateral) at baseline and post-observation. Expectations, pain ratings, and physiological data (e.g., skin conductance level) were collected. A 3×2×2 (group × arm × phase) mixed ANOVA revealed a three-way interaction that confirmed that observational learning modulates pain: F(2,93)=6.08, p=.003, η=.12. Significant baseline-to-post-observation pain increases were shown in the nocebo OBL group, with a bigger increase for the arm with ointment (both p≤.007). In the placebo OBL group, pain was higher for the contralateral relative to the ointment arm (p<.001). Baseline-to-post-observation pain increase was significant for the contralateral arm (p<.001). Expectation mediated these effects. Skin conductance level decreased over time during ointment trials in the nocebo OBL group, suggesting reduced physiological arousal. The findings illustrate that observational learning modulates pain through expectations. In the placebo OBL group, pain did not decrease for the ointment but increased for the contralateral stimuli, which may reflect nocebo learning. Experimental OBL paradigms typically examine relative differences between ointment and contralateral cues. This can complicate disentangling placebo hypoalgesia and nocebo hyperalgesia in laboratory settings. Implications for existing theories are discussed. PERSPECTIVE: Data that systematically compares placebo hypoalgesia and nocebo hyperalgesia induced by observational learning is scarce. The current work illustrates that these effects may be more difficult to disentangle than previously assumed, which could have implications for existing theories on observational learning and placebo effects and their translation to clinical practice.