Somatic Symptom Perception From a Predictive Processing Perspective: An Empirical Test Using the Thermal Grill Illusion.

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 (ß = 0.33, p = .005) and absorption (ß = 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.

Blood pressure and the perception of illusive pain.

Numerous studies have documented an inverse relationship between blood pressure and sensitivity to experimental nociceptive stimulation. The present study aimed to investigate possible associations between blood pressure and the occurrence and intensity of paradoxical pain induced by the thermal grill paradigm. Thirty-one healthy subjects were stimulated three times for 1 min with the nonnoxious temperatures of 15°C and 41°C set at the interlaced cold and warm bars of a water bath-driven thermal grill. Blood pressure and heart rate were recorded concomitantly. On account of previous observations of an association between the sensitivity of the cardiac baroreflex and pain perception, this parameter was additionally obtained. Numerical rating scales were used to quantify subjective pain intensity and pain unpleasantness; subjects were classified as responders and nonresponders to thermal grill stimulation based on pain intensity ratings. Responders exhibited lower systolic and diastolic blood pressure than nonresponders, and inverse linear associations arose between blood pressure and pain intensity and unpleasantness. Baroreflex sensitivity was unrelated to pain ratings. The findings confirmed the hypothesis of a blood pressure dependence of paradoxical pain and support the notion that the cardiovascular and pain regulatory systems interact not only in the processing of pain elicited by noxious input, but also in nonnoxiously generated illusive pain. While this finding is not consistent with the assumption of an involvement of the baroreflex system in mediating the observed interaction, psychological traits and neurochemical factors are alternatively considered.

Rumination and interoceptive accuracy predict the occurrence of the thermal grill illusion of pain.

BACKGROUND: While 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. METHODS: The 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. RESULTS: Logistic 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. CONCLUSION: Our 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.

Beep tones attenuate pain following Pavlovian conditioning of an endogenous pain control mechanism.

Heterotopic noxious counter-stimulation (HNCS) is commonly used to study endogenous pain control systems. The resulting pain inhibition is primarily based on spinal cord-brainstem loops. Recently, functional imaging studies have shown that limbic structures like the anterior cingulate cortex and amygdala are also implicated. Since these structures are involved in learning processes, it is possible that the HNCS-induced pain inhibition may depend on specific cues from the environment that have been associated with pain reduction through associative learning. We investigated the influence of Pavlovian conditioning on HNCS-induced pain inhibition in 32 healthy subjects by using a differential conditioning paradigm in which two different acoustic stimuli were either repeatedly paired or unpaired with HNCS. Series of noxious electrical pulse trains delivered to the non-dominant foot served as test stimuli. Diffuse noxious inhibitory control (DNIC)-like effects were induced by concurrent application of tonic HNCS (immersion of the contralateral hand in ice water). Subjective pain intensity and pain unpleasantness ratings and electromyographic recordings of the facial corrugator muscle and the nocifensive RIII flexion reflex were used to measure changes in pain sensitivity. HNCS induced significant pain and reflex inhibitions. In the post-conditioning phase, only the paired auditory cue was able to significantly reduce pain perceptions and corrugator muscle activity. No conditioned effect could be observed in RIII reflex responses. Our results indicate that the functional state of endogenous pain control systems may depend on associative learning processes that, like in the present study, may lead to an attenuation of pain perception. Similar albeit opposite conditioning of pain control mechanisms may significantly be involved in the exacerbation and chronification of pain states.