Determinants of endogenous analgesia magnitude in a diffuse noxious inhibitory control (DNIC) paradigm: Do conditioning stimulus painfulness, gender and personality variables matter?

Descending modulation of pain can be demonstrated psychophysically by dual pain stimulation. This study evaluates in 31 healthy subjects the association between parameters of the conditioning stimulus, gender and personality, and the endogenous analgesia (EA) extent assessed by diffuse noxious inhibitory control (DNIC) paradigm. Contact heat pain was applied as the test stimulus to the non-dominant forearm, with stimulation temperature at a psychophysical intensity score of 60 on a 0-100 numerical pain scale. The conditioning stimulus was a 60 s immersion of the dominant hand in cold (12, 15, 18 °C), hot (44 and 46.5 °C), or skin temperature (33 °C) water. The test stimulus was repeated on the non-dominant hand during the last 30 s of the conditioning immersion. EA extent was calculated as the difference between pain scores of the two test stimuli. State and trait anxiety and pain catastrophizing scores were assessed prior to stimulation. EA was induced only for the pain-generating conditioning stimuli at 46.5 °C (p = 0.011) and 12 °C (p = 0.003). EA was independent of conditioning pain modality, or personality, but a significant gender effect was found, with greater EA response in males. Importantly, pain scores of the conditioning stimuli were not correlated with EA extent. The latter is based on both our study population, and on additional 82 patients, who participated in another study, in which EA was induced by immersion at 46.5 °C. DNIC testing, thus, seems to be relatively independent of the stimulation conditions, making it an easy to apply tool, suitable for wide range applications in pain psychophysics.