Chapter 6 – EEG imaging 193 Materials and methods Participants Participants of either sex were enrolled in this study. The required sample size for the primary analysis was calculated based on a previous nocebo study 18 that induced nocebo hyperalgesia on thermal pain by use of conditioning, in an MEG paradigm. This study was used merely as an indicator of an appropriate sample size for this comparable study, in lack of a more fitting study to base a power analysis on. Tu et al. (2019) found that a decrease in alpha band connectivity predicted the magnitude of conditioned nocebo hyperalgesia (r = 0.46, p = 0.04). The power analysis was conducted in G*power 3.1 26 for our primary hypothesis. Alpha error probability was set at α = 0.05, and desired power was set at 0.80. With r of 0.46, the sample size indicated was 36 participants. A replacement protocol was used for excluded participants. Inclusion criteria were: age between 18 and 35 years, a good understanding of the English language, and (corrected to) normal vision and hearing. Exclusion criteria were pregnancy or breastfeeding, any pain on the day of testing, having recent injuries on the arms, painful health conditions experienced in the past 6 months, ever having experienced chronic medical or psychiatric conditions, and having consumed psychotropic or analgesic medication, recreational drugs, or more than 3 units of alcohol, in the 24 hours prior to the study appointment. Testing of included participants was discontinued in the case that they would be determined to have too high of a pain threshold (i.e., when thermode maximum temperatures were not sufficient to induce at least moderate pain) or when they would not reliably report a difference (a mean of at least 1.5 on the NRS) between the administered temperatures for control and nocebo trials in the acquisition phase. Participants were recruited through the online website Sona (Sona Systems, Tallinn, Estonia). Study participation involved a 3-hour
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