SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

Supplementary Materials Beyond Conformity: Social Influences on Pain Reports and Physiology By L. Koban & T. D. Wager, 2015, Emotion http://dx.doi.org/10.1037/emo0000087

Supplementary Method Assessment of Individual Differences A long-standing question concerns which individual and personality factors influence placebo effects on pain . Although some traits such as optimism or behavioral activation have been repeatedly associated with placebo, these have not been replicated across different studies and experimental designs. Recently, we suggested that different components of placebo effects (i.e. learning, expectations, instruction, social information) might rely on different underlying neurophysiological mechanisms systems, which may be associated with different personality characteristics . To examine which personality traits were associated with cue and social information effects on pain, we administered several questionnaires, which have previously been associated with individual differences in placebo analgesia or were of specific interest to our questions. The Behavioral Inhibition System/Behavioral Activation System questionnaire (BIS/BAS) consists of four subscales that measure behavioral activation and inhibition and have previously been associated to dopaminergic activity and placebo analgesia . The revised Life Orientation Test (LOT-R) assesses optimism and has also been related to placebo analgesia . In addition, we reasoned that social information effects might be related to individual differences in social desirability (social desirability scale) and empathy (as measured by the Interpersonal Reactivity Index, IRI). To test effects of anxiety, we further assessed trait anxiety (STAI) and pain- related anxiety (Fear of Pain questionnaire, FOP).

Supplementary Results Individual Differences We computed partial correlations (controlling for sex and instruction condition) to explore which personality factors were related to individual differences in the strength of social influence and cue effects on pain. Social influence effects on pain were negatively correlated with the FOP fear of minor pain subscale (r = −.36, p = .004), and positively to optimism (LOT-R, r = .30, p = .019) and the empathic concern subscale of the IRI (r = . 30, p = .017) (see Figure S3). Learning cue effects were significantly negatively correlated with individual differences in the fear of medical pain subscale of the FOP (r = −.26, p = .041) and positively with BAS reward responsiveness (r = .27, p = .035) (see Figure S3). None of the other correlations reached significance.

Supplementary Discussion SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

Individual Differences What drives these important individual differences in social and cue effects on pain? Interestingly, individual differences in the strength of social and conditioned cue effects were related to different personality traits. This is consistent with the suggestion that placebo effects on pain are predicted by person-by-situation interactions . Those participants with the highest conditioned cue effects on pain showed greater trait reward sensitivity, in agreement with previous findings, suggesting an important role of dopaminergic activity in placebo analgesia . In contrast, those with the highest social influences on pain were those high in empathic concern and optimism. Empathy may increase attention to and the estimated value of social information, and interact directly with experienced pain . Further, in line with the present findings, trait optimism has previously been linked to placebo effects . Optimism might be especially important for instructed or social influence effects on pain, which are not reinforced by actual experience , as it was the case in our experiment. Further, optimism might be related to other personality traits that could enhance social influence and placebo effects, such as resilience, extraversion, and trust in other people. Interestingly, both conditioned and social influences on pain were stronger in those with low fear of pain. In line with previous findings , these effects might be due to a generally reduced susceptibility to context information for participants who are afraid of, and therefore potentially very focused on, the painful stimulus itself. Alternatively, participants who are less able to recruit endogenous regulation strategies may also develop increased fear of pain. More research is needed to disentangle the situational factors that interact with individual predispositions to predict differences in endogenous pain regulation . SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

Supplementary Figures

Figure S1

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Figure S1. Significant relationship between expectancy and pain. (A) Individual regression lines between expectancy and pain ratings (every color represents one subject, points depict four bins of data per subject). (B) Individual regression lines depicting the relationship between expectancy and SCR responses to pain. SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

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Figure S2. Time course of expectancy ratings (top) and medium (48°C) heat pain ratings (bottom). Participants learned the association between the two CS and pain over time, whereas the influence of social information on pain expectancy and ratings remained high across the whole duration of the task. SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

Figure S3

Figure S3. Time course of skin conductance responses to heat pain for all eight experimental conditions. To obtain this plot, skin conductance signals were segmented into single trial epochs from −2 to 10 s around heat stimulus onset, baseline corrected, and averaged across trials and individuals for each experimental condition and temperature (see legend within plot, solid lines reflect SOCIALHIGH, dashed lines reflect

SOCIALLOW conditions, temperatures and CS values are color coded). SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

Figure S4

Figure S4. Individual differences in social information influences on pain (top row) are negatively correlated with fear of minor pain (FOP), and positively with trait optimism (LOT-R) and empathic concern (IRI). Individual differences in conditioned cue effects (bottom row) on pain are negatively related to fear of medical pain (FOP) and positively to reward responsiveness (BAS). SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

Figure S5

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Figure S5. Results of the debriefing questionnaire. After the end of the experiment, participants were asked to rate, using a visual analog scale (VAS), “How useful was the information about the other participants’ ratings for predicting pain?” (Usefulness Social) and “How useful were the abstract patterns for predicting pain?” (Usefulness Cues). (A) Mean usefulness ratings were slightly higher for the social information than the cues (t(57) = 2.1, p = .045). (B) Scatter plot for individual ratings of usefulness of social information and of cues. (C) Kernel-smoothed density distribution of usefulness ratings for social information and cues across subjects. Whereas most participants rated the social information as moderately useful, the usefulness ratings for the cues seemed to have a bimodal distribution, indicating that most participants did not find the cues helpful in predicting pain, but a small subgroup of learners found them useful. SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

Figure S6

Figure S6. Results of the control experiment. To exclude the possibility that the expectation ratings were driving the social influence effects pain, we conducted a small control experiment. (A) N = 12 additional healthy participants (nine female, mean age = 26.3 years) performed a learning task that had the same design as our main study, except that participants were not asked to rate their expectations following the social and cue information. (B) The results of this control experiment replicated the previous effects of social information on pain ratings (β = 3.5 [95% CI ± 0.98], t(11) = 7.1, p < .001). Although numerically similar to the results of the main experiment, the effect of the learning cues was not statistically significant (β = 0.5 [95% CI ± 1.72], t(11) = 0.56, p = .58). This is expected, due to the reduced sample size and the fact that the cue effects in the main study were driven by a subgroup of learners. SOCIAL INFLUENCE EFFECTS ON PAIN – Supplementary Materials

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