Chapter 5 – Experimental fear 153 To test warmth and pain threshold levels, heat stimuli were applied on the arm and participants were asked to indicate the first moment at which they perceived warmth and pain, respectively, from a baseline of 32°C. After a practice trial of each, the average of 3 warmth and 3 pain detection values were calculated as the threshold values for warmth and pain, respectively. This method follows published standardized and protocolled procedures 28. Pain calibration protocol and administered stimuli Pain calibrations and selection of pain intensities Pain calibrations were conducted in order to select the temperatures that would be used to induce low, moderate, and high pain in the acquisition and extinction phases (similar to previous studies 5,29). The calibrations were individually tailored, based on participants’ NRS ratings of maximum 30 pain stimuli of varying intensities, ranging from 41°C to 49.9°C. Median temperatures that were rated as low, moderate, and high pain were calculated in order to select temperatures that were consistently given a certain rating. Median temperatures were selected because of the presence of outlier ratings during this early stage of participants receiving pain stimulations of varying intensities. Details of the pain calibration procedure can be found in supplementary material. In the Control and High-threat groups, median temperatures consistently rated and experienced as NRS 1 to 3 were selected and used during control trials, while median temperatures rated as 4 to 6 were used during nocebo trials. In the High-pain group, median temperatures consistently rated as NRS 4 to 6 were used during control trials, while median temperatures rated as 7 to 9 were used during nocebo trials. Consistent with previous nocebo conditioning procedures, lower pain stimulation was administered during control trials and higher pain was
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