• Michael Karl Boettger, David Grossmann, and Karl-Jürgen Bär.
• Institute of Physiology I, Jena, Germany. Karl-Juergen.Baer@med.uni-jena.de
• Psychosom Med. 2013 Apr 1;75(3):281-7.

ObjectiveThe thermal grill illusion (TGI) in which interlacing cold and warm bars create the illusion of a painful sensation has been suggested as an experimental model for central pain states and pain processing. The aim of this study was to use this technique to gain further insights into the altered pain perception in major depressive disorder (MDD).MethodsIn 18 unmedicated patients with MDD, cold and heat pain thresholds (CPT/HPT) as well as the perception of the TGI were examined and compared with 18 matched controls.ResultsCPT and HPT were significantly increased in patients (7.9°C and 47.5°C) compared with controls (15.9°C and 45.2°C, respectively; p < .05). In the range of TGI stimuli that were perceived painful by controls, the patients did not indicate painful sensations, thereby indicating a shift of the stimulus-response curve of TGI pain perception toward higher stimulus intensities, that is, greater temperature differentials between cold and warm bars (11.5°C for controls, 16.7°C for patients). The patients rated the pain intensity perceived at the respective pain thresholds (CPT and HPT) in tendency higher than did the controls, whereas they perceived the TGI less painful despite increased stimulus intensities. Unpleasantness ratings were similar between groups.ConclusionsCPT, HPT and temperature differentials for the perception of the TGI, were increased in patients with MDD as compared with controls. Pain intensity, however, was rated differently for CPT and HPT, where patients indicated higher ratings in tendency, and for the TGI stimulation, where pain was perceived less intense.

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