BackgroundWhile the neurophysiological mechanisms underlying the thermal grill illusion of pain (TGI) have been thoroughly studied, psychological determinants largely remain unknown. The present study aimed to investigate whether cognitive and affective personality traits encompassing rumination, interoception, and suggestibility may be identified as characteristics favouring the elicitation of paradoxical pain experiences.MethodsThe dominant hand of 54 healthy volunteers was stimulated with a water-bath driven thermal grill providing an interlaced temperature combination of 15 and 41°C. Pain intensity and pain unpleasantness perceptions were rated on a combined verbal-numerical scale (NRS). Traits were assessed via questionnaires, the heartbeat-tracking task, and warmth suggestions.ResultsLogistic regression analyses uncovered trait rumination and interoceptive accuracy (IA) as major predictors of the likelihood of the illusive pain occurrence (all p < .05). Rumination and suggestibility had an impact on unpleasant pain perceptions.ConclusionOur findings allowed identifying psychological factors substantially involved in the individual pre-disposition to reporting painful sensations in the thermal grill paradigm. These psychological characteristics may also be relevant in the context of central neuropathic pain, which to a large extent incorporates the same neural pathways.

Objective: In a predictive coding perspective, symptom perceptions result from an integration of pre-existing information in memory with sensory input. Physical symptoms can therefore reflect the relative predominance of either sensory input or pre-existing information. In this study, we used the thermal grill illusion (TGI), which applies interlaced warm and cool temperatures to the skin to create a paradoxical heat-pain experience. Assuming that the TGI compared to single temperature stimulation relies more importantly on an active integration process of the brain to create this paradoxical sensation, we tested the hypothesis whether a manipulation of the expectations during TGI would have more impact than during single temperature stimulation. Methods: Sixty-four participants received different temperature combinations (16/16 °C, 40/40 °C, 16/40 °C) with neutral, positive ("placebo"), and negative ("nocebo") instructions. Subjective stimulus intensity was rated and neuroticism and absorption (openness to absorbing and self-altering experiences) served as potential moderating traits. Results: The TGI condition was rated highest. Overall, negative instructions increased (p < .001, d = 0.58), whereas positive instructions did not significantly change the TGI intensity perception (vs. neutral; p = .144, d = 0.19). In the TGI condition, increased modulation of pain was observed with higher neuroticism (β = .33, p = .005) and absorption (β = 0.30, p = .010). Conclusions: Whereas negative instructions induced a nocebo effect, no placebo effect emerged after positive instructions. The findings are in line with the predictive coding model of symptom perception for participants with higher levels of neuroticism and absorption.