Strong and aversive cold processing and pain facilitation in fibromyalgia patients relates to augmented thermal grill illusion

The thermal grill illusion (TGI) is assumed to result from crosstalk between the thermoreceptive and nociceptive pathways. To elucidate this further, we compared 40 female fibromyalgia patients to 20 healthy women in an exploratory cross-sectional study. Sensations (cold, warm/heat, unpleasantness, pain and burning) evoked by 20 °C, 40 °C and alternating 20 °C/40 °C (TGI) and somatosensory profiles according to standardized quantitative sensory testing (QST) were assessed on the palm of the dominant hand. Compared to healthy controls, fibromyalgia patients reported stronger thermal grill-evoked cold, warm, unpleasantness and pain as well as stronger and more aversive 20 °C- and 40 °C-evoked sensations. They showed a loss in warm, mechanical and vibration detection, a gain in thermal pain thresholds and higher temporal summation (TS). Among QST parameters higher TS in fibromyalgia patients was most consistently associated with an augmented TGI. Independently, an increased TGI was linked to cold (20 °C) but less to warm (40 °C) perception. In fibromyalgia patients all thermal grill-evoked sensations were positively related to a higher 20 °C-evoked cold sensation and/or 20 °C-evoked unpleasantness. In conclusion, the TGI appears to be driven mainly by the cold-input. Aversive cold processing and central pain facilitation in fibromyalgia patients seem to independently augment the activation of the pain pathway.

Cortical oscillatory changes during thermal grill illusion

OBJECTIVE

The thermal grill illusion (TGI) can cause a burning pain sensation when the skin is subjected to simultaneously harmless hot and cold stimuli, and the pain is reported to be similar to central neuropathic pain. Although electroencephalography (EEG) is commonly used in pain research, no reports have revealed EEG activity during TGI.

METHODS

One healthy subject was enrolled, and EEG activity was recorded during the experience of the TGI and a warm sensation. Independent component analysis (ICA) was applied to preprocessed EEG data, which was divided into several clusters.

RESULTS

Theta and alpha bands in the insular cortex and parietal operculum clusters were significantly more desynchronized under the TGI condition than under the warm condition ( P  < 0.05). Additionally, theta, alpha and beta bands in the frontal (middle and inferior frontal gyrus) cluster showed significantly more desynchronization under the TGI condition than under the warm condition ( P  < 0.05).

CONCLUSION

EEG oscillations in these brain areas could be useful markers of central neuropathic pain.

Pain quality of thermal grill illusion is similar to that of central neuropathic pain rather than peripheral neuropathic pain

OBJECTIVES

Application of spatially interlaced innocuous warm and cool stimuli to the skin elicits illusory pain, known as the thermal grill illusion (TGI). This study aimed to discriminate the underlying mechanisms of central and peripheral neuropathic pain focusing on pain quality, which is considered to indicate the underlying mechanism(s) of pain. We compared pain qualities in central and peripheral neuropathic pain with reference to pain qualities of TGI-induced pain.

METHODS

Experiment 1:137 healthy participants placed their hand on eight custom-built copper bars for 60 s and their pain quality was assessed by the McGill Pain Questionnaire. Experiment 2: Pain quality was evaluated in patients suffering from central and peripheral neuropathic pain (42 patients with spinal cord injury, 31 patients with stroke, 83 patients with trigeminal neuralgia and 131 patients with postherpetic neuralgia).

RESULTS

Experiment 1: Two components of TGI-induced pain were found using principal component analysis: component 1 included aching, throbbing, heavy and burning pain, component 2 included itching, electrical-shock, numbness, and cold-freezing. Experiment 2: Multiple correspondence analysis (MCA) and cross tabulation analysis revealed specific pain qualities including aching, hot-burning, heavy, cold-freezing, numbness, and electrical-shock pain were associated with central neuropathic pain rather than peripheral neuropathic pain.

CONCLUSIONS

We found similar qualities between TGI-induced pain in healthy participants and central neuropathic pain rather than peripheral neuropathic pain. The mechanism of TGI is more similar to the mechanism of central neuropathic pain than that of neuropathic pain.

The cornucopia of central disinhibition pain - An evaluation of past and novel concepts

Central disinhibition (CD), as applied to pain, decreases thresholds of endogenous systems. This provokes onset of spontaneous or evoked pain in an individual beyond the ability of the nervous system to inhibit pain resulting from a disease or tissue damage. The original CD concept as proposed by Craig entails a shift from the lateral pain pathway (i.e. discriminative pain processing) towards the medial pain pathway (i.e. emotional pain processing), within an otherwise neurophysiological intact environment. In this review, the original CD concept as proposed by Craig is extended by the primary "nociceptive pathway damage - CD" concept and the secondary "central pathway set point - CD". Thereby, the original concept may be transferred into anatomical and psychological non-functional conditions. We provide examples for either primary or secondary CD concepts within different clinical etiologies as well as present surrogate models, which directly mimic the underlying pathophysiology (A-fiber block) or modulate the CD pathway excitability (thermal grill). The thermal grill has especially shown promising advancements, which may be useful to examine CD pathway activation in the future. Therefore, within this topical review, a systematic review on the thermal grill illusion is intended to stimulate future research. Finally, the authors review different mechanism-based treatment approaches to combat CD pain.

The Cerebral Localization of Pain: Anatomical and Functional Considerations for Targeted Electrical Therapies

Millions of people in the United States are affected by chronic pain, and the financial cost of pain treatment is weighing on the healthcare system. In some cases, current pharmacological treatments may do more harm than good, as with the United States opioid crisis. Direct electrical stimulation of the brain is one potential non-pharmacological treatment with a long history of investigation. Yet brain stimulation has been far less successful than peripheral or spinal cord stimulation, perhaps because of our limited understanding of the neural circuits involved in pain perception. In this paper, we review the history of using electrical stimulation of the brain to treat pain, as well as contemporary studies identifying the structures involved in pain networks, such as the thalamus, insula, and anterior cingulate. We propose that the thermal grill illusion, an experimental pain model, can facilitate further investigation of these structures. Pairing this model with intracranial recording will provide insight toward disentangling the neural correlates from the described anatomic areas. Finally, the possibility of altering pain perception with brain stimulation in these regions could be highly informative for the development of novel brain stimulation therapies for chronic pain.

Dynamics and Perception in the Thermal Grill Illusion

A basic challenge in perception research is to understand how sensory inputs from physical environments and the body are integrated in order to facilitate perceptual inferences. Thermal perception, which arises through heat transfer between extrinsic sources and body tissues, is an integral part of natural haptic experiences, and thermal feedback technologies have potential applications in wearable computing, virtual reality, and other areas. While physics dictates that thermal percepts can be slow, often unfolding over timescales measured in seconds, much faster perceptual responses can occur in the thermal grill illusion. The latter refers to a burning-like sensation that can be evoked when innocuous warm and cool stimuli are applied to the skin in juxtaposed fashion. Here, we show that perceptual response times to the thermal grill illusion decrease systematically with perceived intensity. Using results from behavioral experiments in combination with a physics-based description of tissue heating, we develop a simple model explaining the perception of the illusion through the evolution of internal tissue temperatures. The results suggest that improved understanding of the physical mechanisms of tissue heating may aid our understanding of thermal perception, as exemplified by the thermal grill illusion, and might point toward more efficient methods for thermal feedback.

Ineffectiveness of tactile gating shows cortical basis of nociceptive signaling in the Thermal Grill Illusion

Painful burning sensations can be elicited by a spatially-alternating pattern of warm and cold stimuli applied on the skin, the so called "Thermal Grill Illusion" (TGI). Here we investigated whether the TGI percept originates spinally or centrally. Since the inhibition of nociceptive input by concomitant non-nociceptive somatosensory input has a strong spinal component, we reasoned that, if the afferent input underlying the TGI originates at spinal level, then the TGI should be inhibited by a concomitant non-nociceptive somatosensory input. Conversely, if TGI is the result of supraspinal processing, then no effect of touch on TGI would be expected. We elicited TGI sensations in a purely thermal condition without tactile input, and found no evidence that tactile input affected the TGI. These results provide further evidence against a spinal mechanism generating the afferent input producing the TGI, and indicate that the peculiar burning sensation of the TGI results from supraspinal interactions between thermoceptive and nociceptive systems.

Sex differences in thermal detection and thermal pain threshold and the thermal grill illusion: a psychophysical study in young volunteers

Background

Sex-related differences in human thermal and pain sensitivity are the subject of controversial discussion. The goal of this study in a large number of subjects was to investigate sex differences in thermal and thermal pain perception and the thermal grill illusion (TGI) as a phenomenon reflecting crosstalk between the thermoreceptive and nociceptive systems. The thermal grill illusion is a sensation of strong, but not necessarily painful, heat often preceded by transient cold upon skin contact with spatially interlaced innocuous warm and cool stimuli.

Methods

The TGI was studied in a group of 78 female and 58 male undergraduate students and was evoked by placing the palm of the right hand on the thermal grill (20/40 °C interleaved stimulus). Sex-related thermal perception was investigated by a retrospective analysis of thermal detection and thermal pain threshold data that had been measured in student laboratory courses over 5 years (776 female and 476 male undergraduate students) using the method of quantitative sensory testing (QST). To analyse correlations between thermal pain sensitivity and the TGI, thermal pain threshold and the TGI were determined in a group of 20 female and 20 male undergraduate students.

Results

The TGI was more pronounced in females than males. Females were more sensitive with respect to thermal detection and thermal pain thresholds. Independent of sex, thermal detection thresholds were dependent on the baseline temperature with a specific progression of an optimum curve for cold detection threshold versus baseline temperature. The distribution of cold pain thresholds was multi-modal and sex-dependent. The more pronounced TGI in females correlated with higher cold sensitivity and cold pain sensitivity in females than in males.

Conclusions

Our finding that thermal detection threshold not only differs between the sexes but is also dependent on the baseline temperature reveals a complex processing of “cold” and “warm” inputs in thermal perception. The results of the TGI experiment support the assumption that sex differences in cold-related thermoreception are responsible for sex differences in the TGI.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-017-0147-5) contains supplementary material, which is available to authorized users.

Thermal referral: evidence for a thermoceptive uniformity illusion without touch

When warm thermal stimulators are placed on the ring and index fingers of one hand, and a neutral-temperature stimulator on the middle finger, all three fingers feel warm. This illusion is known as thermal referral (TR). On one interpretation, the heterogenous thermal signals are overridden by homogenous tactile signals. This cross-modal thermo-tactile interaction could reflect a process of object recognition, based on the prior that many objects are thermally homogenous. Interestingly, the illusion was reported to disappear when the middle digit was lifted off the thermal stimulator, suggesting that tactile stimulation is necessary. However, no study has investigated whether purely thermal stimulation might induce TR, without any tactile object to which temperature can be attributed. We used radiant thermal stimulation to deliver purely thermal stimuli, which either were or were not accompanied by simultaneous touch. We found identical TR effects in both the original thermo-tactile condition, and in a purely thermoceptive condition where no tactile object was present. Control experiments ruled out explanations based on poor spatial discrimination of warm signals. Our purely thermoceptive results suggest that TR could reflect low-level organization of the thermoceptive pathway, rather than a cognitive intermodal modulation based on tactile object perception.

Deficits in pain perception in borderline personality disorder: results from the thermal grill illusion

Supplemental Digital Content is Available in the Text.

The thermal grill illusion is reduced in borderline personality disorder. This suggests that the deficits in pain perception in this group are of central origin.

It is well documented that borderline personality disorder (BPD) is characterized by reduced pain sensitivity, which might be related to nonsuicidal self-injury and dissociative experiences in patients with BPD. However, it remains an open question whether this insensitivity relies at least partly on altered sensory integration or on an altered evaluation of pain or a combination of both. In this study, we used the thermal grill illusion (TGI), describing a painful sensation induced by the application of alternating cold and warm nonnoxious stimuli, in patients with either current or remitted BPD as well as matched healthy controls. Two additional conditions, applying warm or cold temperatures only, served as control. We further assessed thermal perception, discrimination, and pain thresholds. We found significantly reduced heat and cold pain thresholds for the current BPD group, as well as reduced cold pain thresholds for the remitted BPD group, as compared with the HC group. Current BPD patients perceived a less-intense TGI in terms of induced pain and unpleasantness, while their general ability to perceive this kind of illusion seemed to be unaffected. Thermal grill illusion magnitude was negatively correlated with dissociation and traumatization only in the current BPD patients. These results indicate that higher-order pain perception is altered in current BPD, which seems to normalize after remission. We discuss these findings against the background of neurophysiological evidence for the TGI in general and reduced pain sensitivity in BPD and suggest a relationship to alterations in N-methyl-D-aspartate neurotransmission.