LAUSR

Using the thermal grill illusion and a predictive coding framework, this study shows that somatosensory perception can be increased by negative verbal instructions and that this effect is stronger in poorly versus clearly defined sensory stimuli, moderated by neuroticism and absorption. The thermal grill illusion serves as a valuable experimental model to investigate the relative contribution of central versus peripheral input to somatic perception and could be used to investigate pathogenetic mechanisms of chronic pain. ABSTRACT Objective In a predictive processing perspective, symptom perceptions result from an integration of preexisting information in memory with sensory input. Physical symptoms can therefore reflect the relative predominance of either sensory input or preexisting 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 with 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 factors. 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 (versus neutral; p = .144, d = 0.19). In the TGI condition, increased modulation of pain was observed with higher neuroticism (β = 0.33, 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 processing model of symptom perception for participants with higher levels of neuroticism and absorption.