236 Behavioral results The regression assumptions of linearity and homogeneity were met, and behavioral data were normally distributed. No outliers were present, determined by Mahalanobis distance. Correlation analyses of psychological questionnaire scores (Table 1) did not yield significant associations with nocebo magnitude or any other pain measures (all p > 0.05). Results on the between-groups mediating effect of questionnaire scores on nocebo magnitudes also yielded non-significant results (for all paths p ≥ 0.05). Baseline and post-experimental learning rates are shown in Table 1 and indicate that WMS learning rates remained stable from before to after DCS administration. The nocebo manipulation successfully induced nocebo responses as measured during the first trials of extinction (Figure 2A). Across both groups, there was a significant difference between pain reports for the first nocebo and first control trial of the extinction phase (F (1,49) = 73.03, p < 0.001, ηp 2 = 0.19) indicating the presence of nocebo hyperalgesia. We also found a significant nocebo effect in the first five pairs of extinction trials which were used as an evocation phase for fMRI analysis (F (1,49) = 59.73, p < 0.001, ηp 2 = 0.08; Figure 2B). Finally, there was significant extinction of nocebo responses, with the magnitude of nocebo responses being significantly lower in the last pair of (nocebo/control) extinction trials, as compared to the first pair of extinction trials (F (1,49) = 13.17, p = 0.001, ηp 2 = 0.08). Pharmacological manipulation A mixed ANOVA indicated that there was no significant interaction between drug group and the magnitude of nocebo responses based on trial type (F (1,48) = 0.002, p = 0.97, ηp 2 < 0.001; Figure 2C). This was aligned with no increases in learning rate from pre to post drug
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