Conditioning stimulus for PPR

CPT consisted of the immersion of the right arm up to the shoulder, for a maximum of two minutes, into a bath of cold water. A refrigerated circulation system (Julabo F33-HL heating/refrigerating circulators) kept the water at a constant 10°C throughout the experiment. The temperature was chosen to be painful yet tolerable for two minutes (27). During the administration of the conditioning stimulus, participants were instructed to report verbally pain intensity and pain unpleasantness on a scale of 0 (no pain) to 100 (worst pain imaginable/most unpleasant imaginable) at the beginning, then at 30-second intervals up to 120 s. Throughout the manuscript, we refer to this conditioning stimulus as CPT-PPR.

To illustrate the PPR phenomenon, we provided an example like the one used in a previous study (9). Participants were asked to imagine themselves walking in a −30°C snowstorm for 20 min and finally arriving home to feel the warmth of the air inside the house. This heat would induce feelings of both relief and pleasure (9) elicited by the cessation of the painful stimulus. To assess the PPR, participants were asked to rate it on a scale of 0 [“I feel relief, but no pleasure”] to 100 [“I feel relief and the most intense pleasure possible”]. PPR was measured immediately after the end of the immersion and every 30 s afterwards for four minutes. These ratings were used to calculate the mean, the first (score at CPT offset) PPR and the peak (highest score) PPR of each participant.