160 nocebo responses after acquisition (primary outcome measure) was defined as the difference between the first nocebo and the first control trial of the extinction phase. The first extinction trials were selected since the intensity of administered pain was identical in nocebo and control trials in this phase, and previous studies show the clearest effect of nocebo responses in those trials 27,41. The magnitude of nocebo responses at the end of extinction was defined as the difference between the last nocebo and the last control trial of the extinction phase. The reduction of nocebo responses was measured as the change in magnitude of nocebo responses (nocebo minus control) between the start and the end of the extinction phase. One-way ANOVAs were used to assess mean between-groups differences in warmth and pain thresholds, temperatures used to induce pain, and NRS pain ratings during the experiment. Fear outcome measures The magnitude of self-reported fear levels was measured withinsubjects, and was defined as the difference in fear ratings for nocebo trials compared to control trials of the acquisition or the extinction phase. Fear-potentiated eyeblink startle responses were analyzed according to typical pre-processing of EMG recordings in the PhysioData Toolbox for Matlab 42. The EMG signal was digitized at 1000 Hz, Boxcar filtered, rectified, and each startle trial was segmented. Peak amplitudes were computed, defined as the maximum of the response curve within 21 to 300 milliseconds after startle probe onset. All startle waveforms were also manually inspected and technical abnormalities or artifacts were eliminated. Each peak amplitude was scored by subtracting it from its baseline score (averaged EMG level between 1 and 20 milliseconds after the probe onset). Finally, raw scores were transformed to T-scores, to account for inter-individual variation
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