Mia Thomaidou

Chapter 7 – Pharmacological fMRI 225 Sensory thresholds We followed a sensory-thresholds method that follows published standardized and protocolled procedures 38. To test warmth and pain threshold levels, heat stimuli were applied from a baseline of 32°C on the forearm and participants were asked to indicate the first moment that they perceived warmth and the first moment that they perceived pain. After a practice trial for each, the average of 3 warmth and 3 pain detection values were calculated as thresholds for warmth and pain, respectively. Pain calibration and administered stimuli Throughout the experiment, each stimulus was initiated from a 32°C baseline, increased to a target temperature with ramp up and return rates of 8°C per second, and presented at peak temperature for 5 seconds. The maximum temperature that could be reached was 50°C. The interstimulus interval consisted of a pain rating screen with a 6 second duration followed by a fixation cross with a mean duration of 5 seconds, jittered around a normal distribution of ±2 seconds. Pain calibrations were conducted to select the temperatures that would induce moderate and high pain during nocebo conditioning. The calibrations were individually tailored, based on participants’ NRS ratings of maximum 30 pain stimuli of varying intensities. We used the median temperatures that participants consistently rated as NRS 6 to 9 (high pain) for nocebo trials in the pre-conditioning and acquisition phases. We used median temperatures consistently rated as approximately NRS 3 to 5 (moderate pain) for all control trials as well as extinction nocebo trials. After calibrations, a nocebo pre-conditioning took place and included 7 nocebo and 7 control trials, to increase the time of learning and ensure nocebo effects would be induced. At the start of the MRI session a

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