116 Sensory thresholds To test warmth and pain threshold levels, heat stimuli were applied and participants were asked to indicate the first moment at which they perceived warmth and the first moment they perceived pain. The average of 3 warmth detection values and 3 heat pain detection values were determined as the threshold values for warmth and pain respectively. This method followed published standardized and protocolled procedures 26. Pain calibration protocol and administered stimuli Pain calibrations were conducted in order to select the temperatures that would be used to induce low, moderate, and high pain in phases 1 and 2. The calibrations were individually tailored, based on the NRS ratings of 42 heat stimuli of varying intensities, as well as participants’ bodily and facial reactions to pain stimuli. For the calibration procedure as well as throughout the experiment, each stimulus was initiated from a 32°C baseline, increased to a target temperature, and presented for 4 seconds, excluding a ramp up rate of 8°C per second and a return rate of 8°C per second. The inter-stimulus interval was 8 seconds. Median temperatures consistently rated and experienced as NRS 2 to 3 were selected and used to induce low pain, median temperatures rated as NRS 4 to 6 were used to induce moderate pain, and median temperatures rated as NRS 7 to 8 were used to induce high pain. During induction and during attenuation, 15 nocebo and 15 control stimuli were administered in pseudorandom order, so that no three stimuli of the same type were administered in a row. During each of the two evocations, 5 nocebo and 5 control stimuli were administered in pseudorandom order. To reduce habituation to heat-pain, the thermode was moved twice (mid-way through phases 1 and 2) to a more proximal site on the same arm.
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