Sad mood increases pain sensitivity upon thermal grill illusion stimulation: Implications for central pain processing

Abstract

In different fields of neuroscience research, illusions have successfully been used to unravel underlying mechanisms of stimulus processing. One such illusion existing for the field of pain research is the so-called thermal grill illusion. Here, painful sensations are elicited by interlacing warm and cold bars, with stimulus intensities (temperatures) of these bars being below the respective heat pain or cold pain thresholds. To date, the underlying mechanisms of this phenomenon are not completely understood. There is some agreement, however, that the sensation evoked by this stimulation is generated by central nervous interactions. Therefore, we followed two approaches in this study: firstly, we aimed at developing and validating a water-driven device which might be used in fMRI scanners in future studies - subject to minor adaptations. Secondly, we aimed to interfere with this illusion by induction of a sad mood state, a procedure which is suggested to influence central nervous structures that are also involved in pain processing. The newly developed device induced thermal grill sensations similar to those reported in the literature. Induction of sad, but not neutral mood states, resulted in higher pain and unpleasantness ratings of the painful illusion. These findings might be of importance for the understanding of pain processing in healthy volunteers, but putatively even more so in patients with major depressive disorder. Moreover, our results might indicate that central nervous structures involved in the affective domain or cognitive domain of pain processing might be involved in the perception of the illusion.

Evidence for Thalamic Involvement in the Thermal Grill Illusion: An fMRI Study

“…A better understanding of the mechanisms involved in such distressful symptoms may translate into improved treatment. To this end, the TGI has been studied with regard to pharmacologic [11], [12], multi-sensory [13] and affective [14] manipulations and, recently, we reported of a putative genetic component relating to variation in thermal-pain sensitivity [15].…”

Thermal grill conditioning: Effect on contact heat evoked potentials

“…Increased arousal related to the TGI may then explain, in part, facilitated CHEPs. Increased arousal has been reported in response to the TGI34. In this previous study, greater arousal was related to more unpleasantness34.…”

“…Increased arousal has been reported in response to the TGI34. In this previous study, greater arousal was related to more unpleasantness34. In order to explain the facilitation of CHEPs, because there was no relationship between unpleasantness and increases in N1 and N2P2 amplitude, the TGI would have had to increase arousal in “non-responders”.…”

“…If, and only if, a subject indicated unpleasantness or pain, they were then asked to rate the pain/unpleasantness by means of a numeric rating scale ranging from 0 (not unpleasant/painful at all) to 10 (very unpleasant or most unbearable pain). We believe that this is an important distinction from studies that cue subjects to rate unpleasantness/pain without first identifying if the sensation was unpleasant/painful34. Independent of their reported perception, all individuals were asked to describe the various modalities from a list of descriptors (e.g., warm, burning, cool, freezing, sharp, itching, and unpleasant).…”

Rise of the Sensors: Nociception and Pruritus

“…This suggests that these additional brain areas are involved in central nociceptive sensitization processes. Prior experience with cold-induced pain or allodynia [34] and affective dysfunction [35] may also worsen the intensity of pain perceptions and these other central responses. It will be of interest to determine if similar findings occur in nonallergic rhinopathy defined by environmental or experimental cold air sensitivity [36].…”