The role of stimulation parameters on the conditioned pain modulation response.

Background and purpose Conditioned pain modulation (CPM) is a testing paradigm representing features of diffuse noxious inhibitory control. There is large diversity in the paradigms applied to induce CPM, and the consistency in CPM responses assessed by different paradigms is largely unknown. We aimed to characterize and explore the associations between the CPM responses assessed by different paradigms in the same cohort. Methods Thirty-three healthy middle-aged subjects underwent six CPM paradigms. The 'test-stimuli', consisted of thermal and mechanical modalities, using pain thresholds, suprathreshold pain and temporal summation types of measurements. The 'conditioning-stimulus' consisted of a contact heat stimulus applied to the thener of the left hand for 60s at an intensity of 46.5°C. Results Large variability was observed among the responses to the different CPM paradigms. Surprisingly, no correlations were found between the various CPM responses. Conclusions The variability in the CPM responses may suggest that the capacity of pain modulation is a multifaceted trait, whose expression varies with the application of different CPM paradigms. Implications Considering that CPM responses may represent different processes when assessed by different paradigms, we encourage the use of more than one CPM paradigm.