226 baseline phase took place during which 5 high and 5 moderate pain stimuli were administered. The acquisition and extinction phases each included 14 nocebo and 14 control trials. All trials were administered in pseudorandom order, so that no more than three trials of the same type were administered in a row. To reduce habituation or sensitization to heat-pain, we moved the thermode higher on the arm between functional scans; the thermode was moved to a more proximal site on the same arm after baseline and at one third and two thirds of the acquisition/extinction procedure). Nocebo manipulation A commercial Transcutaneous Electrical Nerve Stimulation (TENS) device (Beurer EM 80) was used to deliver (sham) electrical stimuli, which served as the nocebo manipulation in the procedure. Negative verbal suggestions were used to create expectations regarding the painenhancing effects of administering electrical stimuli in combination with thermal pain. Two electrodes were placed in a diagonal line on the base of the thumb and the inner elbow. Participants underwent a short mock calibration procedure during which they felt a light electrical pulse through the electrodes (ConMed MR-compatible Cleartrace ECG electrodes). This pulse was delivered in order to increase the believability of the nocebo manipulation. The device was not actually present during conditioning in the MRI scanner, but messages displayed on a computer monitor via E-Prime 3.0 (Psychology Software Tools, Pittsburgh, PA, USA) indicated the sham activation of the electrical stimulation during nocebo trials. Negative suggestions indicated to all participants that when the messages “on” (nocebo stimulus in either purple or yellow font, counterbalanced) and “off” (control stimulus in grey font) were displayed, their pain would be respectively aggravated (nocebo trials) or not altered (control trials). In the pre-conditioning and acquisition
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