Chapter 6 – EEG imaging 211 Table 2. Summary of statistics for differences in EEG parameters between nocebo during evocation and baseline high pain shown in Figure 4. EEG parameter Electrode MdnBHP MdnNOC Z p Relative power alpha WBA 13.91 ± 1.84 19.11 ± 1.72 -3.51 0.0005 Relative power beta WBA 19.24 ± 1.19 17.83 ± 1.13 0.51 0.61 Relative power gamma WBA 9.37 ± 0.92 5.96 ± 0.79 3.28 0.001 DFA alpha WBA 0.68 ± 0.01 0.69 ± 0.01 -1.31 0.19 DFA beta WBA 0.73 ± 0.01 0.68 ± 0.01 3.14 0.0017 DFA gamma WBA 0.81 ± 0.02 0.72 ± 0.01 3.76 0.0002 Note: Wilcoxon signed-rank tests were performed on the whole-brain average per subject (computed as mean of all electrodes). Rows show EEG parameters, columns show the median whole-brain average value across subjects for control and nocebo trials, Z- and Pvalue corresponding to the signed-rank test. The median EEG parameter value for each group is reported with the standard error of the mean. BHP: Baseline high pain, NOC: Nocebo trials during evocation. Bold font weight indicates significance at P < 0.05. Discussion This study provides a novel characterization of the electrophysiological phenotype of nocebo hyperalgesia using EEG. Spectral and temporal dynamics of brain oscillations were studied at baseline, during restingstate pre- and post- measurements and during nocebo acquisition and evocation. The main findings of this study are (i) a negative correlation between LRTC of beta oscillations and the magnitude of nocebo hyperalgesia, (ii) a positive correlation between baseline LRTC and magnitude of nocebo hyperalgesia, (iii) alpha and beta power suppression during nocebo conditioning, and (iv) biomarker differences between the experience of high pain at baseline and the experience of nocebo-augmented pain.
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