Article

The thermal grill illusion and what is painful about it

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The 'thermal grill illusion' refers to paradoxical sensations of heat and pain, resulting from simultaneous application of interlaced warm and cold stimuli to the skin. It provides an interesting model of integrative mechanisms in the nervous system, supposed to be relevant in explaining the hypersensitivity found in chronic pain of unclear etiology. The aim of this study is to investigate the perceptual qualities elicited by a reconstruction of the original grill stimulator and to compare these qualities with those elicited by a single temperature thermode of identical dimensions. Healthy participants performed these comparisons by choosing adjectives describing the perceived sensory qualities. We hypothesized that the thermal grill would be perceived as different from a single temperature hot stimulus near pain threshold because of varying sensory qualities. Moreover, the qualities elicited by the grill were expected to be different from the qualities elicited by its single component temperatures. The thermal grill elicited a complex percept, which was distinguished almost perfect from a hot stimulus. The pattern of perceived qualities of the thermal grill differed from single temperature warm and hot stimuli. Pain-related sensations were less present in the grill percept than in a single hot stimulus near pain threshold. The spectrum of qualities of the grill stimulus changed marginally with stimulus duration by decrease of a cold component and concurrent increase of a heat component. In conclusion, the percept of the thermal grill is not simply pain--it can be understood as a metaesthetic percept at the transition from heat to pain.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... T HERMAL grill illusion (TGI) phenomenon involves the concurrent application of warm and cold stimuli to the skin, eliciting sensations of burning and pain [1] [2] [3]. This phenomenon facilitates the induction of pain sensations through non-damaging temperature stimuli [4] [5] and finds applications in simulating pain within virtual reality environments [6], as well as in suppressing itch [7]. TGI is known to induce a burning pain sensation as well as a sensation similar to cold freezing pain [4] [8]. ...
... This phenomenon facilitates the induction of pain sensations through non-damaging temperature stimuli [4] [5] and finds applications in simulating pain within virtual reality environments [6], as well as in suppressing itch [7]. TGI is known to induce a burning pain sensation as well as a sensation similar to cold freezing pain [4] [8]. ...
... For example, Lam et al. discovered that a pronounced TGI was generated by heating the ends of three bars while cooling the central bar [27]. Nonetheless, variations in the number of rods in a row (2)(3)(4)(5)(6) and the spacing between them (1-10 mm) were observed to pose negligible impact on TGI perception [28]. To date, the precise placement of hot and cold stimuli necessary to induce a robust TGI response remains to be conclusively determined. ...
Article
Full-text available
This study proposes a novel approach to elicit the thermal grill illusion (TGI)—a phenomenon characterized by the concurrent application of hot and cold stimuli to the skin that causes sensations of pain and burning. Contrary to conventional techniques that manipulate heat physically through Peltier elements or water, our method employs chemicals, namely, capsaicin and menthol, to activate transient receptor potential ion channels. This approach perceptually conveys hot and cold sensations and synergistically induces TGI. Notably, the proposed technique offers both energy efficiency and compactness, enhancing its suitability for practical applications. We conducted three experiments to validate the effectiveness of the proposed technique. Experiment 1 aimed to ascertain the feasibility of inducing TGI by contrasting sensations produced individually and collectively by each chemical, targeting to elicit both hot and cold sensations. Experiment 2 focused on exploring the impact of temporal disparities in the application of chemicals inducing hot and cold sensations on TGI induction. Experiment 3 investigated the correlation between the positioning of stimulus sites, delivering warmth and cold sensations, and the intensity of the resultant TGI. The findings demonstrate that adjacent applications of capsaicin and menthol can successfully generate TGI. Moreover, the intensity of TGI can be modulated by varying the time interval between the applications of these two chemicals and altering the locations of the stimuli. Specifically, a more pronounced TGI was achieved by applying capsaicin on the proximal side and menthol on the distal side of the forearm. These results hold promise for practical implementations, particularly in developing itch-suppressing patches.
... Focusing on the pain quality described by subjects experiencing TGI-induced pain, the TGI paradigm was originally developed to create synthetic heat perception and TGI-induced pain is frequently described as "burning" [5]. Other terms including aching, throbbing, sharp, and itching were sporadically reported in small numbers of subjects [17][18][19]. In the present study, we analyzed and characterized the pain qualities of TGI-induced pain. ...
... Discussion TGI-induced pain is an experience of misperception actualizing synthetic pain without any nociceptive input in the periphery. Our participants most frequently described TGI-induced pain as hot-burning in accord with previous reports [17,24,38]. In addition to hot-burning pain, TGI-induced pain was also characterized as cold-freezing pain, which is also consistent with previous studies [17,24,38]. ...
... Our participants most frequently described TGI-induced pain as hot-burning in accord with previous reports [17,24,38]. In addition to hot-burning pain, TGI-induced pain was also characterized as cold-freezing pain, which is also consistent with previous studies [17,24,38]. Therefore, our custom-built TGI device is valid and provided equivalent data to previous studies. ...
Article
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.
... Our idea was to use the itch-relief effect of heat pain at a harmless temperature for treatment of the itch sensation. We focused on the phenomenon called the thermal grill illusion (TGI) [3,4], which is also called synthetic heat [5]. This illusion is a well-known perceptual phenomenon that induces pain or burning sensations without damaging the skin through the simultaneous presentation of hot and cold stimuli to the skin. ...
... For each trial, they were asked to choose words that described the sensation they felt from the following: cool, cold, warm, hot, stinging, itching, tickling, wet, painful, good feeling, strange feeling. Some of these words (cool, cold, warm, hot, tickling, stinging, painful) were taken from previous works on nocuous temperature sensation [3,9]. Other words (itching, wet, good feeling, strange feeling) were responses given by other participants in our preliminary experiments. ...
... What made the alternate-temperature condition different from the other conditions were the descriptions "painful" and "strange feeling", the rates of which were 22.5% and 32.5%, respectively. These are typical expressions for the known TGI, and we may thus say that the device can partly deliver the TGI; the rates were similar to those observed in previous work [3]. ...
Article
Painful thermal stimulation is known to inhibit the itch sensation, which is a significant problem for many diseases. We focused on the thermal grill illusion, which is well-known phenomenon that can generate pain or a burning sensation without physical damage; we tried to achieve a similar effect via thermal stimulation at a harmless temperature. We have developed a roller-type itch-relief device. When the device is rolled on the user's skin, the skin is alternately exposed to hot and cold stimuli. In addition, vibration is applied so that a virtual scratching feeling is presented without damaging the skin. This paper evaluates the device by eliciting an itch using a lactic acid solution and then applying the device. Results show that the device is effective in terms of relieving the itch sensation, and the effect continued for 8 minutes.
... The application to the skin of spatially interlaced innocuous warm and cool temperature bars in the form of a thermal grill device (TG) usually produces a thermal sensation that is distinctly different from, and more intense than, the thermal sensations evoked by either of the component stimuli alone (Thunberg, 1896;Burnett and Dallenbach, 1927). This percept has generally been identified as painful (Green and Pope, 2003;Bouhassira et al., 2005;Leung et al., 2005;Kern et al., 2008a,b), described as qualitatively similar to the burning of cold pain (Craig, 1998), and is frequently termed a paradoxical illusion of pain (Bouhassira et al., 2005;Leung et al., 2005;Defrin et al., 2008;Kern et al., 2008a,b;Li et al., 2009), although the designation of the percept as painful still remains controversial (Green, 2002;Bach et al., 2011). Many details regarding the percept are lacking, and the mechanisms giving rise to it need to be further elucidated. ...
... Some investigators have described the TG-induced percept as transient (Leung et al., 2005) and others as persistent and taking 20-30 s to stabilize (Bouhassira et al., 2005) and/or that the quality of the percept varied depending upon the stimulus duration (Alston, 1920;Leung et al., 2005;Bach et al., 2011;Averbeck et al., 2013). However, the quality and intensity of the percept has never been investigated systematically and quantitatively, and most authors have required the subject to report the nature of the percept after the completion of, but not during, the thermal stimulation. ...
... As well, similar to the WARM and COOL stimuli, the TG was rated more unpleasant than painful, which is consistent with the findings of other studies (Alston, 1920;Lindstedt et al., 2011a,b;Averbeck et al., 2013). Taken together, these findings support the observations of Bach et al. (2011), that the TG stimulus induces a unique and unpleasant thermal percept. ...
Article
Background The application to the skin of spatially interlaced innocuous warm (40 °C) and cool (20 °C) thermodes (termed a thermal grill - TG) can produce an unusual thermal percept, but the mechanisms remain unclear.Methods We compared the percept quality and intensity over a 120-s period evoked by each of three configurations of a 6-bar thermal stimulator (6TS): all 40 °C(WARM); all 20 °C(COOL); alternating bars 40/20 °C (TG) at two body sites (forearm and palm).ResultsBoth unpleasantness and pain were significantly greater for the TG-induced (vs. either COOL- or WARM-induced) percept. Unpleasantness ratings were significantly higher than pain intensity ratings. Several emotional qualitative descriptors were unique to the TG-induced percept. TG palmar (vs. forearm) stimulation produced a more intense percept and was perceived as painful in more subjects. Temporal profiles of intensities of TG-induced percepts differed from those induced by the COOL or WARM thermodes alone. For both unpleasantness and pain, the site differences in the temporal profile were also unique for TG versus the COOL- or WARM-evoked percepts. Qualitative characteristics of the TG-induced percept varied over time and between subjects.Conclusions The TG percept intensity and temporal profile were different from those evoked by either of its component parts. The perceived quality is person-specific. These differences suggest that the classic ‘TG illusion’ results from complex central integration of several types of peripheral afferent inputs activated by the TG. Differing body site-related roles of thermosensory afferents in discrimination versus temperature homeostasis may explain site-related variations in the percept.
... The TGI manifests as a burning sensation elicited by interlaced innocuous cold and warm stimuli on the skin [4,5]. Counterintuitively, this spatial alternation does not result in the perception of each individual stimulus independently, but instead gives rise to a new, qualitatively distinct sensation characterized by unique attributes of combined hot, cold and burning sensations [6]. The perception of the TGI is thus, set apart from the sensations elicited by the individual stimuli generating it, indicating the existence of underlying sensory mechanisms that govern thermo-nociceptive interactions [7,8]. ...
... Characteristically, the TGI manifests as pronounced burning sensations, accompanied by enhanced perception of warmth or cold [6][7][8]35]. We showed that burning sensations increased in magnitude depending on the specific isoprobability curve (increasing from 25% to 50% and 75%) and that thermosensory qualities varied depending on both the quartile (increased heat progressing from the first to the second and the third quartiles) and the improbability curve (increased heat progressing from 25% to 50% and 75%) from which the temperature pairs were sampled. ...
Preprint
Full-text available
In the thermal grill illusion (TGI), the spatial alternation of non-noxious warm and cold temperatures elicits burning sensations that resemble the presence of noxious stimuli. Previous research has largely relied on the use of specific temperature values (i.e., 20°C and 40°C) to study this phenomenon in both healthy individuals and patient populations. However, this methodology fails to account for inter-individual differences in thermal sensitivity, limiting the precision with which TGI responses can be evaluated across diverse populations. To address this gap, we created a Two-Dimensional Thermal Grill Calibration (2D-TGC) protocol, enabling an efficient and precise estimation of the combinations of warm and cold temperatures needed to elicit burning sensations tailored to each individual. By applying the 2D-TGC protocol in 43 healthy participants, we demonstrated key findings: (1) The TGI can be thresholded using an adaptive psychophysical method. (2) Multiple combinations of warm and cold temperatures can elicit this phenomenon. (3) The protocol facilitated the identification of temperature combinations that elicit TGI with varying levels of probability, intensity, and perceived quality ranging from freezing cold to burning hot. (4) TGI responsivity can be quantified as a continuous variable, moving beyond the conventional classification of individuals as responders vs. non-responders based on arbitrary temperature values. The 2D-TGC offers a comprehensive approach to investigate the TGI across populations with altered thermal sensitivity, and can be integrated with other methods (e.g., neuroimaging) to elucidate the mechanisms responsible for perceptual illusions in the thermo-nociceptive system.
... The thermal grill illusion (TGI), first introduced in 1896, is the perception of burning heat and pain that arises from the simultaneous cutaneous application of a grill with interlaced warm (38-42 • C) and cool (18)(19)(20)(21)(22) • C) bars [1][2][3]. Although cold and warm cutaneous stimulations are felt as coolness and warmth in isolation, respectively, their spatial combination (when placing a hand on the interlaced grill) often creates a thermonociceptive prickling sensation (burning heat and pain) [1][2][3]. ...
... The thermal grill illusion (TGI), first introduced in 1896, is the perception of burning heat and pain that arises from the simultaneous cutaneous application of a grill with interlaced warm (38-42 • C) and cool (18)(19)(20)(21)(22) • C) bars [1][2][3]. Although cold and warm cutaneous stimulations are felt as coolness and warmth in isolation, respectively, their spatial combination (when placing a hand on the interlaced grill) often creates a thermonociceptive prickling sensation (burning heat and pain) [1][2][3]. ...
Article
Full-text available
The thermal grill illusion (TGI) is a paradoxical perception of burning heat and pain resulting from the simultaneous application of interlaced warm and cold stimuli to the skin. The TGI is considered a type of chronic centralized pain and has been used to apply nociceptive stimuli without inflicting harm to human participants in the study of pain mechanisms. In addition, the TGI is an interesting phenomenon for researchers, and various topics related to the TGI have been investigated in several studies, which we will review here. According to previous studies, the TGI is generated by supraspinal interactions. To evoke the TGI, cold and warm cutaneous stimuli should be applied within the same dermatome or across dermatomes corresponding to adjacent spinal segments, and a significant difference between cold and warm temperatures is necessary. In addition, due the presence of chronic pain, genetic factors, and sexual differences, the intensity of the TGI can differ. In addition, cold noxious stimulation, topical capsaicin, analgesics, self-touch, and the presence of psychological diseases can decrease the intensity of the TGI. Because the TGI corresponds to chronic centralized pain, we believe that the findings of previous studies can be applied to future studies to identify chronic pain mechanisms and clinical practice for pain management.
... This leads to a sensation of strong, but not necessarily painful, heat often preceded by transient cold [9]. Several studies indicate that the TGI is a very complex phenomenon that is generated by central higher order processing and reveals a relationship between the thermoreceptive and nociceptive systems [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Thus, sex differences in thermoreception and thermal pain perception may be related to sex differences in the TGI. ...
... In the present study thermal grill stimulation (20/40°C interleaved) of the hand induced a unique perception including sensations of warmth, coldness, unpleasantness, burning, stinging, prickling and pain. Consistent with the literature, the present study shows the TGI to be very complex [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. A novel finding in the present study was that the TGI is also sex-dependent. ...
Article
Full-text available
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.
... Although many researchers have found that the TGI is painful to a majority of participants, others have debated the painfulness of the TGI and the involvement of the nociceptive system in generating the illusion (Fruhstorfer et al., 2003;Bach et al., 2011). Furthermore, a recent study reported that the TGI is not painful in cats (Boettger et al., 2016), calling into question the translatability of Craig and Bushnell's (1994) physiological findings. ...
... While the painfulness of the TGI has been questioned (Fruhstorfer et al., 2003;Bach et al., 2011), our results are in agreement with those of many others showing that interlacing warm and cool bars are capable of producing pain (Craig and Bushnell, 1994;Craig et al., 1996;Bouhassira et al., 2005;Leung et al., 2005;Defrin et al., 2008;Kern et al., 2008a,b;Li et al., 2009;Boettger et al., 2011Boettger et al., , 2013Boettger et al., , 2016Lindstedt et al., 2011a,b). Three subjects (17%) did not, however, report any TGI pain during the Control run, confirming previous findings of some TGI-insensitive individuals (Bouhassira et al., 2005;Kern et al., 2008a,b;Boettger et al., 2016). ...
Article
Background: The thermal grill illusion (TGI) refers to the perception of burning heat and often pain that arises from simultaneous cutaneous application of innocuous warm and cool stimuli. This study utilized conditioned pain modulation (CPM) to help elucidate the TGI's underlying neural mechanisms, including the debated role of ascending nociceptive signals in generating the illusion. Methods: To trigger CPM, subjects placed the left hand in noxious cold (6 °C) water before placing the right volar forearm onto a thermal grill. Lower pain and unpleasantness ratings of the grill in this CPM run compared to those in a control run (i.e. 33 °C water) were taken as evidence of CPM. To determine whether CPM reduces noxious heat pain and illusory heat pain equally, an experimental group of subjects rated pain and unpleasantness of a grill consisting of innocuous alternating warm (42 °C) and cool (18 °C) bars, while a control group rated a grill with all bars controlled to a noxious temperature (45 °C). Results: CPM produced significant and comparable reductions in pain, unpleasantness and perceived heat of both noxious heat and the TGI. Conclusions: This result suggests that the TGI results from signals in nociceptive dorsal horn convergent neurons, since CPM involves descending inhibition with high selectivity for this neuronal population. More broadly, CPM's ability to produce a shift in perceived thermal sensation of both noxious heat and the TGI from 'hot' to 'warm' implies that nociceptive signals generated by a cutaneous stimulus can contribute to its perceived thermal intensity. Significance: Conditioned pain modulation reduces the perceived painfulness, unpleasantness and heat of the thermal grill illusion and noxious heat similarly. The results have important theoretical implications for both types of pain.
... We chose perceived temperature as a dependent variable, because it gives continuous, quantitative data, is commonly reported in nociceptive sensations using thermal grill stimulation [1,6], has been reliably used before in matching tasks [7], and reflects the same continuous, underlying mechanism as pain judgment [5]. Moreover, temperature matching avoids the methodological difficulties, notably suggestion effects, that occur when applying verbal labels such as ''pain'' to the unusual sensory quality of thermal grill stimuli [8]. ...
... What implications do our findings have for pain? Our stimulation produced the characteristic nociceptor-mediated sensation of burning heat found with several other TGI stimuli [1,7,8,16]. However, we preferred not to ask participants to judge pain explicitly, for methodological reasons. ...
Article
The relation between pain perception and spatial representation of the body is poorly understood. In the thermal grill illusion (TGI), alternating non-noxious warm and cold temperatures cause a paradoxical, sometimes painful, sensation of burning heat [1]. We combined thermal grill stimulation with crossing the fingers to investigate whether nociceptively mediated sensation depends on the somatotopic or spatiotopic configuration of thermal inputs. We stimulated the index, middle, and ring fingers when the middle finger either was or was not crossed over the index to generate "warm-cold-warm" patterns in either somatotopic or spatiotopic coordinates. Participants adjusted a temperature delivered to the other hand until it matched their perception of the cold target finger (index or middle). We found significant temperature overestimation when the target was central within the spatial configuration (warm-cold-warm) compared to when it was peripheral (cold-warm-warm). Crucially, this effect depended on the spatiotopic configuration of thermal inputs, but it was independent of the finger posture and present for both index and middle target fingers-the thermal grill effect for the middle finger was abolished when it was crossed over the index to adopt a spatiotopically peripheral position, while the same effect was newly generated for the index finger by the same postural change. Our results suggest that the locations of multiple stimuli are remapped into external space as a group; nociceptively mediated sensations depended not on the body posture, but rather on the external spatial configuration formed by the pattern of thermal stimuli in each posture. Copyright © 2015 Elsevier Ltd. All rights reserved.
... The thermal grill illusion (TGI), first described by Thunberg in 1886, means a strong, not necessarily painful, but often unpleasant sensation of heat evoked by an interleaved application of innocuous cool and warm stimuli [1][2][3][4] . Parts of the contact area can also be perceived as cool 5 . This phenomenon is thought to be based on a crosstalk between central thermoreceptive and nociceptive pathways 6 , albeit mechanisms are still discussed controversially. ...
Article
Full-text available
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.
... The illusion of heat, also known as synthetic heat 7-10 , refers to non-painful heat sensations evoked by the thermal grill 6,[11][12][13][14] . The illusion of pain, which is the most recognised aspect of the TGI, is the distinctive burning sensation that accompanies the simultaneous presentation of cold and warm stimuli 1,2,15 . The hallmark of both illusory components is a qualitative change in perception when the cold and warm stimuli are applied concurrently, compared to when they are presented individually. ...
Preprint
Full-text available
The Thermal Grill Illusion (TGI), a phenomenon in which the juxtaposition of innocuous warm and cold temperatures on the skin elicits a burning sensation, offers a unique perspective to how pain occurs in response to harmless stimuli. We investigated the role of the spinal cord in the generation of the TGI across two experiments (total n = 80). We applied heat and cold stimuli to dermatomes, areas of skin innervated by a single spinal nerve, that mapped onto adjacent or nonadjacent spinal segments. Enhanced warm and burning ratings during the TGI were observed when cold and warm stimuli were confined within the same dermatome. Further, heat perception was enhanced when the cold stimulus projected to the segment caudal to the warm stimulus, compared to the opposite spatial arrangement. Our results are consistent with spatial spread and integration of thermosensory information in the spinal cord.
... Accordingly, TGI-associated pain is considered as a pure central phenomenon. [1][2][3][4][5][6] Over the last decade, this phenomenon has evoked considerable interest among researchers. Several studies were conducted in the fields of psychiatric diseases or elucidate sex-based differences to evaluate the application of TGI responses and further unravel this phenomenon. ...
Article
Full-text available
Purpose This study aimed to use thermal grill illusion (TGI), an experimental model of pain processing and central mechanisms, to evaluate the perception of TGI-related sensations or pain in patients with chronic lower back pain (CLBP). Patients and Methods The perception of TGI (warmth/heat, cold, unpleasantness, pain, burning, stinging, and prickling) was examined in 66 patients with CLBP and compared with that in 22 healthy participants. The visual analog scale (VAS) scores for CLBP, Oswestry Disability Index (ODI), and 12-Item Short Form Survey (SF-12) scores were obtained from the included patients with CLBP. Results The CLBP group showed a less intense perception of TGI for sensations of warmth/heat, unpleasantness, and pain than the control group. The CLBP group felt burning sensations lesser than the control (2.77 vs 4.55, P=0.016). In the CLBP group, there were significant correlations between the ODI and the degree of unpleasantness (r=0.381, P=0.002) and prickling sensation (r=0.263, P=0.033). There were also significant correlations between the mental component score of the SF-12 and the degree of warmth/heat (r=−0.246, P=0.046), unpleasantness (r=−0.292, P=0.017), pain (r=−0.292, P=0.017), and burning sensations (r=−0.280, P=0.023). Conclusion Our results may be useful for clinicians to evaluate the effectiveness of drugs or interventions to manage centralized LBP.
... Our hypothesis was based on the assumption that paradoxical pain perceptions in response to unusual thermal grill input implying simultaneous stimulation with two innocuous, interlaced warm and cool temperatures, reflects the integrative work of the brain to create a meaningful experience to a higher degree compared to simultaneous stimulation with two identical warm or cool stimuli. Supporting this assumption, a qualitative study showed that the TGI is perceived as a complex, ambiguous percept integrating various perceptual qualities (43,44). Along these lines, in a post-hoc calculation comparing the equality of coefficients of variation (45), we observed the largest standard deviations for the intensity ratings in the TGI condition compared to both control conditions (cool vs. TGI, p < .001; ...
Article
Somatic symptoms are a central feature of most mental and physical disorders. According to Bayesian predictive coding, symptom perceptions result from integrating expectations and current sensory input. Imprecise sensory input should be more vulnerable to top down influence than precise sensory input. The thermal grill illusion (TGI) provides an ambiguous sensory experience, in which interlaced warm and cool temperatures lead to an unusual, sometimes painful sensation. To test hypotheses derived from a Bayesian predictive coding framework of somatic symptom perception, we verbally induced placebo and nocebo effects during the TGI. 64 healthy participants received different temperature combinations with a thermal grill device (16/16°C, 40/40°C, 16/40°C) in three different conditions, neutral, positive, and negative instruction, and rated subjective intensity of the thermal stimulation. Neuroticism and absorption were assessed as potential moderating traits. Participants perceived 16/40°C as most intense (compared to 16/16°C: p<.001, d=1.12; compared to 40/40°C: p<.001, d=1.23). Negative instructions increased perceived intensity (p<.001, d=0.58), whereas positive instructions did not change the sensation compared to the neutral instruction (p=.144, d=0.19). Neuroticism (β=.33, p=.005) and absorption (β=0.30, p=.010) significantly predicted increased modulation via negative instruction of 16/40°C compared to the control temperatures. Whereas the nocebo instruction increased the temperature perception, no placebo effect emerged. The central hypothesis derived from Bayesian predictive coding that the induction of negative expectations is able to bias particularly low-precise somatosensory input was supported for participants with higher levels of neuroticism and absorption. The TGI can serve as a laboratory model for somatic symptom perceptions in healthy participants.
... Since these seminal observations, the "thermal grill illusion" (TGI) has been described extensively using various modern stimulating devices. Of defining characteristics, the TGI is reported as a uniquely "unpleasant" somatosensory experience [1][2][3][4][5][6][7][8] . Central disinhibition related to persistent activation in polymodal nociceptive spinothalamic cells, coupled with reductions of activity in innocuous thermoreceptive spinothalamic cells has been proposed as underlying the unpleasantness of the TGI 6,9,10 . ...
Article
Full-text available
The ‘thermal grill illusion’ (TGI) is a unique cutaneous sensation of unpleasantness, induced through the application of interlacing warm and cool stimuli. While previous studies have investigated optimal parameters and subject characteristics to evoke the illusion, our aim was to examine the modulating effect as a conditioning stimulus. A total of 28 healthy control individuals underwent three testing sessions on separate days. Briefly, 15 contact heat stimuli were delivered to the right hand dorsum, while the left palmar side of the hand was being conditioned with either neutral (32 °C), cool (20 °C), warm (40 °C), or TGI (20/40 °C). Rating of perception (numeric rating scale: 0–10) and evoked potentials (i.e., N1 and N2P2 potentials) to noxious contact heat stimuli were assessed. While cool and warm conditioning decreased cortical responses to noxious heat, TGI conditioning increased evoked potential amplitude (N1 and N2P2). In line with other modalities of unpleasant conditioning (e.g., sound, visual, and olfactory stimulation), cortical and possibly sub-cortical modulation may underlie the facilitation of contact heat evoked potentials.
... In contrast to the wealth of information regarding tactile spatial and temporal illusions, there has been substantially less research on illusions involving the thermal sensory system. One of the few illusions that has been studied is the thermal grill illusion which refers to the burning pain sensation that can result from touching interlaced warm (36-42 ⁰C) and cool (18-24 ⁰C) stimuli [54][55][56]. When touched individually such stimuli are perceived to be innocuous. ...
Thesis
This thesis studied the effect of different stimulus parameters on the thermal response of the skin. A set of thermal patterns, known as thermal icons, was presented to participants using a thermal display mounted on the hand. The thermal responses of the skin were studied to understand which features of the thermal stimuli were important and could be perceived by users. The effectiveness of these patterns was evaluated for applications involving hand-held and wearable thermal devices. In the first series of experiments, a set of six thermal icons was developed and presented on the thenar eminence and the fingertips. The second experiment was conducted on the wrist with a revised set of thermal icons which had a shorter duration and were presented relative to each participant's baseline skin temperature. The information transfer (IT) values for the thermal icons presented on the wrist-mounted thermal display demonstrated that the information processing capabilities of the thermal sensory system may rival those achieved with vibrotactile inputs. To date, thermal icon studies have only used the temporal properties of stimuli and not the spatial properties. A set of two experiments was conducted to examine how the spatial and temporal properties of thermal stimuli interact. The results showed that the temporal properties of thermal stimulation can influence the perceived location of a thermal stimulus. This space-time dependency for the thermal sensory system provides an extra dimension to use to present information in a thermal display and potentially could result in a display that functionally has a higher spatial resolution than the number of thermal elements would indicate.
... For instance, so-called multimodal C2 fibers have been associated with the sensation of the thermal grill illusion in humans [19], yet their occurrence, distribution and characteristics in animals is not well understood. Alternatively, the cold, heat and pain components which are being integrated in the thermal grill perception in humans [20] may have a different physiological importance in different animal species, e.g. considering that animals are used to moving on a cold floor. ...
Article
Simultaneous presentation of alternating innocuous warm and cold stimuli induces in most humans a painful sensation called thermal grill illusion (TGI). Here, pain is elicited although nociceptors are not activated. Upon back-translation of behavioral correlates from humans to animals, we found that neither cats nor rodents show adverse reactions when exposed to TGI stimulation. These results question that a TGI observed as a pain-related change in behavior can be elicited in animals. While distinct neuronal patterns as previously reported may be measurable in animals upon TGI stimulation, their translational meaning towards the sensation elicited in humans is unclear.
... These items were taken from a previous study on pain qualities during the TGI. 3 Finally, the participants were asked to indicate the general intensity of pain perceived during the trial using a 100-mm visual analog scale (VAS) ranging from "no pain" to "worst pain imaginable." ...
Article
It is well documented that borderline personality disorder (BPD) is characterized by reduced pain sensitivity, which might be related to non-suicidal self-injury and dissociative experiences in BPD patients. 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 the present study, we used the thermal grill illusion (TGI), describing a painful sensation induced by the application of alternating cold and warm non-noxious 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 to the HC group. Current BPD patients perceived a less intense TGI in terms of induced pain as well as unpleasantness, while their general ability to perceive this kind of illusion appeared to be unaffected. TGI 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 appears 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.
... Since pain was not reported by all subjects nor was it the dominant quality of sensations reported, we avoided rating scales associated with pain and instead instructed subjects to rate thermal intensity. Justification for the rating of thermal sensations comes from a recent report by Bach et al. (2011), indicating that grill sensations encompass a metaesthetic percept at the transition from heat to pain. Indeed, the most frequent sensations reported in response to grill stimulation are not pain descriptors but instead cold and heat sensations. ...
Article
Background: Thunberg's thermal grill produces a sensation of strong heat upon skin contact with spatially interlaced innocuous warm and cool stimuli. Methods: To examine the classes of peripheral axons that might contribute to this illusion, the effects of topical l-menthol, an activator of TRPM8, and cinnamaldehyde, a TRPA1 agonist, on the magnitude of thermal sensations were examined during grill stimulation in healthy volunteers. Results: Under control conditions, cutaneous grill stimulation (interlaced 20/40 °C) evoked a sensation of heat, and for individual subjects, the magnitude of this heat sensation was positively correlated with cold pain threshold (CPT). Menthol increased the CPT and enhanced the magnitude of grill-evoked heat. Cinnamaldehyde intensified warm sensations, reduced heat pain threshold and also enhanced grill-evoked heat. Conclusions: Both TRPM8-expressing and TRPA1-expressing afferent axons can affect grill-evoked thermal sensations. The enhancement of grill-evoked sensations of temperature with menthol and cinnamaldehyde may provide an additional clinically relevant means of testing altered thermal sensitivity, which is often affected in neuropathic patient groups.
Article
Full-text available
Thermal illusions, a subset of haptic illusions, have historically faced technical challenges and limited exploration. They have been underutilized in prior studies related to thermal displays. This review paper primarily aims to comprehensively categorize thermal illusions, offering insights for diverse applications in thermal display design. Recent advancements in the field have spurred a fresh perspective on thermal and pain perception, specifically through the lens of thermal illusions.
Article
Background and introduction: Pain is a subjective phenomenon, that is often misunderstood and invalidated. Despite recent advances in health professional training, it remains unclear how students should be taught about the subjectivity of pain. This study explored how a novel teaching activity that integrated physiotherapy students' first-hand experiences with laboratory-induced pain could address this gap. Objective: The study aimed to explore the experiences and perceptions of physiotherapy students in relation to a workshop where physiotherapy students experienced laboratory induced pain. Methods: We used a descriptive qualitative research design. Eighteen students participated in interviews. Transcripts were analyzed using an inductive conventional content analysis. Results: We identified four overarching themes: 1) First-hand pain experiences facilitated engagement in learning; 2) Reflecting on these personal and peer pain experiences helped students make sense of pain; 3) The learning activity helped students understand the inherent subjectivity and complexity of pain; and 4) Students saw benefits for clinical practice. Conclusion: Integrating first-hand pain experiences within entry-level physiotherapy training appears to have novel value in helping students understand pain subjectivity. Future research should use robust and controlled designs to explore how this novel approach can be used to facilitate further understanding and empathy within clinical interactions with people living with pain.
Article
Paradoxical heat sensation (PHS) and the thermal grill illusion (TGI) are both related to the perception of warmth or heat from innocuous cold stimuli. Despite being described as similar perceptual phenomena, recent findings suggested that PHS is common in neuropathy and related to sensory loss, while TGI is more frequently observed in healthy individuals. To clarify the relationship between these two phenomena, we conducted a study in a cohort of healthy individuals to investigate the association between PHS and TGI. We examined the somatosensory profiles of 60 healthy participants (34 females, median age 25 years) using the quantitative sensory testing (QST) protocol from the German Research Network on Neuropathic Pain. The number of PHS was measured using a modified thermal sensory limen (TSL) procedure where the skin was transiently pre-warmed (max 43.5°C and min 35.7°C), or pre-cooled (max 28.8°C and min 15.0°C) before the PHS measure. This procedure also included a control condition with a pre-temperature of 32°C. The number of TGI responses was quantified during simultaneous application of warm and cold innocuous stimuli. All participants had normal thermal and mechanical thresholds compared to the reference values from the QST protocol. Only two participants experienced PHS during the QST procedure. In the modified TSL procedure, we found no statistically significant differences in the number of participants reporting PHS in the control condition (N = 6) vs. pre-warming (N = 3; min = 35.7°C, max = 43.5°C) and pre-cooling (N = 4, min = 15.0°C, max = 28.8 °C) conditions. Fourteen participants experienced TGI, and only one participant reported both TGI and PHS. Individuals with TGI had normal or even increased thermal sensation compared to individuals without TGI. Our findings demonstrate a clear distinction between individuals experiencing PHS or TGI, as there was no overlap observed when using identical warm and cold temperatures that were alternated either temporally or spatially. While PHS was previously related to sensory loss, our study revealed that TGI is associated with normal thermal sensitivity. This suggests that an efficient thermal sensory function is essential in generating the illusory sensation of pain of the TGI.
Article
Introduction: Cerebral projections of nociceptive stimuli are of great interest as targets for neuromodulation in chronic pain. To study cerebral networks involved in processing noxious stimuli, researchers often rely on thermo-nociception to induce pain. However, various limitations exist in many pain-inducing techniques, such as not accounting for individual variations in pain and trial structure predictability. Methods: We propose an improved and reliable psychometric experimental method to evaluate human nociceptive processing to overcome some of these limitations. The developed testing paradigm leverages a custom-built, open-source, thermoelectric device (TED). The device construction and hardware are described. A maximum-likelihood adaptive algorithm is integrated into the TED software, facilitating individual psychometric functions representative of both hot and cold pain perception. In addition to testing only hot or cold thresholds, the TED may also be used to induce the thermal grill illusion (TGI), where the bars are set to alternating warm and cool temperatures. Results: Here, we validated the TED's capability to adjust between different temperatures and showed that the device quickly and automatically changes temperature without any experimenter input. We also validated the device and integrated psychometric pain task in 21 healthy human subjects. Hot and cold pain thresholds (HPT, CPT) were determined in human subjects with <1°C of variation. Thresholds were anticorrelated, meaning a volunteer with a low CPT likely had a high HPT. We also showed how the TED can be used to induce the TGI. Conclusion: The TED can induce thermo-nociception and provide probabilistic measures of hot and cold pain thresholds. Based on the findings presented, we discuss how the TED could be used to study thermo-nociceptive cerebral projections if paired with intracranial electrode monitoring.
Article
Full-text available
Purpose/Aim The thermal grill illusion is a paradoxical pain sensation induced by simultaneous exposure to spatially separated, non-painful, cold, and warm stimuli. This study aimed to determine whether paradoxical sensations are also evoked by simultaneous exposure to painful cold-heat stimuli and whether the mechanism involves modulation by segmental and extra-segmental spatial integration. Materials and Methods Sensory perceptions were triggered by simultaneous application of painful cold-heat pulse stimuli using a developed bedside tool equipped with quantitative thermal stimulator devices. Four conditions were investigated: (1) one device placed on the forearm (condition 1, control); (2) two devices placed on the forearm (condition 2, ipsilateral segmental integration); (3) two devices placed on the forearm and ipsilateral thigh (condition 3, extra-segmental integration); and (4) two devices placed bilaterally on the forearms (condition 4, contralateral segmental integration). The evoked perceptions of paradoxical heat sensation and the loss of cold or heat sensation were evaluated. Results The aforementioned phenomena were experienced by 11(35.4%), 3(9.7%), 3(9.7%), and 0(0.0%) subjects for conditions 1–4, respectively. Fisher's exact test revealed significant differences (p=.001) among the four conditions. However, Bonferroni post hoc analysis revealed significant differences only between conditions 1 and 4 (p=.005). Conclusions Simultaneous painful cold–heat pulse stimulation can induce paradoxical sensations similar to those shown for non-painful thermal (cold and heat) stimuli. They were predominantly evoked by ipsilateral integration. Paradoxical sensations have diagnostic value, and quantifying them using a simple bedside tool may be useful in the clinical setting.
Article
The thermosensory system may misidentify a temperature stimulus with different thermal properties. The mechanism of this hot-cold confusion has not been clarified; hence, it has not yet been applied. In this study, we created a wearable temperature presentation device that is closer to the application and analyzed the tendency and mechanism of temperature confusion by analyzing the hot-cold confusion of temperature sensation in the fingers, which are most frequently in contact with objects. Two experiments were performed. In the first experiment, we presented stimuli on the tips of three fingers (first, second, and third fingers). In the second experiment, we presented stimuli at the center of the distal phalanx, middle phalanx, and proximal phalanx of the first finger. The experimental results indicated the occurrence of hot-cold confusion. Domination, in which the center is dominated by both ends, and a mutual effect, in which the center interacts with both ends, were observed.
Article
Full-text available
We focused on the inverse thermal sensation caused by the presence of both hot and cold stimuli, which we named hot-cold confusion. Some researchers have shown that when participants touch a thermal stimulus simultaneously with two opposite thermal stimuli on both sides, the outer temperatures dominate the center temperature; for example, a hot stimulus between two cold stimuli is perceived as cold. However, there has not been sufficient research on the effect of the center stimulus on the outer stimuli. In the current study, we placed a participant's forearm on an alignment where hot and cold stimuli were alternately placed in three locations and found that the participants sometimes selected the inverse thermal sensation of the presented surface not only at the center but also at the outer locations. Namely, opposite thermal stimuli applied at multiple locations affected each other, and the participants sometimes perceived the hot stimulus at the outer location as cold even when the two of three stimuli were hot, and vice versa. In addition, using various alignments of thermal stimuli, we revealed a directional bias of the effect from the cold stimulus and a difference in strength according to its location on the forearm.
Article
Full-text available
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.
Article
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.
Conference Paper
Thermal referral (TR) and thermal grill illusion (TGI), known as illusions of thermal sensation, have been well studied. In a previous study, an experiment using two thermal-tactile stimulations to the forearm revealed that these illusions simultaneously occurred. In this experiment result, a few subjects perceived a hot stimulation as a cold sensation and/or a cold stimulation as a hot sensation. This paradoxical phenomenon of thermal sensation, which is not discussed specifically in the previous study, could be a fatal problem in the case presenting thermal stimulation on multiple spots intentionally. Therefore, we decided to analyze this paradoxical phenomenon. In this paper, we confirmed that this phenomenon occurs when we present thermal stimulation on two spots and three spots. In comparing the results of thermal stimulation on two spots and three spots, the occurred probability increased on three spots.
Conference Paper
The objective of this experiment was to determine whether illusions of space and time that have been demonstrated for mechanical stimulation on the skin also occur for thermal stimuli within the innocuous range of temperatures. Four cooling pulses were presented on the forearm in varying spatial and temporal sequences. Participants indicated the perceived location of the first two pulses in the four-pulse sequence after each trial. The results indicate that the position of the second pulse changed substantially in the direction of the third pulse when the interval between the pulses was brief (0.2 s) and the distance between the second and third pulse was larger. At longer intervals and shorter distances there was no change in perceived location. These findings demonstrate that the tau effect does occur with thermal stimuli, and that the temporal interval between thermal stimuli applied to the skin can influence their perceived location.
Chapter
We found that force or tactile sensation occurred when temperature of thermal elements which were statically touched by subject’s skin changes rapidly. This study aims to clarify its mechanism and to investigate its nature. In this paper, we conducted an experiment to verify incidence rate and quality of this thermal-tactile illusion. As result of the experiment, some kind of vertical sensation occurred and interpretations of occurred sensation were various.
Article
Experimental and clinical observations of interactions between the nociceptive and thermoceptive systems have suggested that they could be part of the homoeostatic system relating to the condition of the body, described as 'interoception'. Homoeostatic physiological systems are extensively interconnected. Thus, consistent with this hypothesis, we would expect thermoregulatory challenges to be associated with changes in pain perception. The effects of whole-body warming or cooling inducing significant changes in mean body temperature were tested in 15 healthy volunteers (29 ± 6 years old) on: (i) the paradoxical burning pain induced by the application of simultaneous non-noxious thermal stimuli with a 'thermal grill' and (ii) the 'normal' pain evoked by noxious thermal stimuli. Whole-body warming and cooling induced changes in opposite direction of the threshold of the paradoxical pain induced by the thermal grill, consisting of an increase by 1.2 ± 1.7 °C (p = 0.02) during the warming session and a nonsignificant decrease by 0.7 ± 2.7 °C (p = 0.15) during the cooling session. In addition, there was a correlation (r = 0.54; p = 0.002) between the magnitude of the change in mean body temperature and the magnitude of the change in the threshold of the paradoxical pain induced by the thermal grill. By contrast, the thermal challenges induced no significant change in pain evoked by noxious hot or cold stimuli. Our results are consistent with the notion that pain has a homoeostatic (interoceptive) dimension and showed that the thermal grill-induced pain is a unique experimental model to investigate this differentiable pain dimension. © 2015 European Pain Federation - EFIC®
Article
The thermal grill illusion (TGI), where interlaced warm and cold bars cause an unusual burning sensation, and paradoxical heat sensations (PHS), where cold is perceived as warm when alternating warm and cold, are examples of a complex integration of thermal sensations. Here we investigated the effect of sensitization of heat-sensitive neurons on cold and warm integration. We examined thermal thresholds, PHS, and warm, cold, and pain sensations to alternating cold (10°C) and warm (40°C) bars (the thermal grill, TG) in the primary area (application site) after topical application with capsaicin and vehicle control (ethanol) on the volar forearms in randomized order in 80 healthy participants. As expected capsaicin induced heat allodynia and hyperalgesia and decreased cold and cold pain sensation. In addition, we found that after capsaicin application, the TG caused less pain and burning than the 40°C bars alone in contrast to the control side where the TG caused more pain and burning consistent with the TGI. In both situations, the pain intensity during the TG correlated inversely with both cold and warm pain thresholds but not detection thresholds. PHS was only seen in 3 participants after control application but in 19 participants after capsaicin. Those with PHS after capsaicin application had higher detection thresholds to both cold and warm than those without PHS, but there was no difference in thermal pain threshold. These results suggest that a complex crosstalk among several cold and warm sensitive pathways shapes thermal perception.
Conference Paper
When thermal stimulation is applied to one location on the skin and tactile stimulation is presented to another, we perceive the thermal sensation on the latter location as well. While this illusion, known as thermal referral, has been well studied, there is little knowledge on the mutual interaction among multiple thermal-tactile stimuli. We conducted an experiment for verifying the mutual interaction of thermal referral between two thermal-tactile stimuli on forearm and found that there are strong asymmetry between the stimuli locations and between the thermal conditions. The elbow side perceives more thermal referral and synthetic heat (thermal grill illusion) than the wrist side. The warm sensation tends to spread from the periphery toward the center, whereas the cool sensation tends to spread from the center toward the periphery.
Article
The simultaneous application of innocuous cutaneous warm and cold stimuli with a "thermal grill" can induce both paradoxical pain and paradoxical warmth ('heat'). The goal of this study was to investigate further the relationships between these paradoxical sensations. Stimuli were applied to the palm of the right hands of 21 volunteers with a thermode consisting of six bars, the temperature of which was controlled by Peltier elements. We assessed the quality and intensity of the sensations evoked by series of stimuli consisting of progressively colder temperatures combined with a series of given warm temperatures. We applied a total of 116 series of stimuli, corresponding to 785 combinations of warm and cold temperatures. The two paradoxical phenomena were reported for most of the series of stimuli (n = 66). In each of these series, the two phenomena occured in the same order: paradoxical warmth followed by paradoxical pain. The difference between the cold-warm temperatures eliciting paradoxical warmth was significantly smaller than that producing paradoxical pain. The intensities of the warmth and unpleasantness evoked by the stimuli were directly related to the magnitude of the warm-cold differential. Our results suggest that there is a continuum between the painful and non painful paradoxical sensations evoked by the thermal grill, which may share pathophysiological mechanisms. These data also confirm the existence of strong relationships between the thermoreceptive and nociceptive systems and the utility of the thermal grill for investigating these relationships.
Conference Paper
An itch is a significant problem for many diseases and relief of itch without side effect is required. We focused on the fact that painful thermal stimulation inhibits the itch sensation. Based on two well-known phenomena, thermal grill illusion and synthetic heat, which can generate pain or burning sensation without physical damage, we tried to achieve similar effect with harmless-range thermal stimulation.We developed a roller-type itch-relief device. The roller is composed of two parts. One part is set hot and the other is set cold by embedded Peltier devices. When the device is rolled on the user's skin, the skin is exposed to hot and cold stimuli alternatively. We also evaluated the elicited sensation and confirmed that it could partly deliver pain sensation.
Conference Paper
Painful thermal stimulation is known to inhibit itch, which is a significant problem in many diseases. We focused on thermal grill illusion and synthetic heat, which are well-known phenomena that can generate pain or burning sensation without physical damage; we tried to achieve a similar effect via a harmless-range thermal stimulation. We developed a roller-type itch-relief device. When the device is rolled onto the user's skin, the skin is alternately exposed to hot and cold stimuli. The roller is composed of an aluminum pipe cut into two parts along the longitudinal axis. One part is set to hot and the other is set to cold by embedded Peltier devices. When the device is rolled on the user's skin, the skin is alternately exposed to hot and cold stimuli. In addition, vibration is applied so that a virtual scratching feeling is presented without damage to the skin. We evaluated the device by eliciting an itch using a lactic acid solution and then applying the device. The results showed that the device provides effective temporal relief from itch and that its effect continues for a few minutes.
Article
Full-text available
Cold temperature can evoke a wide spectrum of perceptual sensations that range from freshness to unpleasant cold or overt pain. In mammals, the detection of cold temperature is accomplished by the activation of different subsets of sensory terminals innervating the skin and mucosae. Direct recordings of corneal nerve endings, combined with studies of thermoreceptive neurons in culture, have allowed the characterization of ionic mechanisms involved in cold temperature sensing. In recent years, major progress has also taken place in the identification and operation of thermally gated ion channels, especially of the transient receptor potential (TRP) family. However, it is still uncertain how individual sensory endings can be activated with different thermal thresholds. In this review, we have considered the known properties of cold-sensitive receptors and their transduction mechanisms and related them to the sensations they evoke. We analyzed the evidence linking specific ion channels to the activation of particular sets of afferent fibers. In our view, cold thermotransduction is complex and involves the concerted operation of several ion channels. Excitatory effects of cationic channels (e.g., TRPs) balance their activity with several excitability brakes (e.g., potassium channels), leading to tunable levels of sensory thresholds and activity. Alteration in this fine balance may result in altered cold sensitivity, a frequent symptom in patients with peripheral nerve injury.
Article
Full-text available
We investigated the role of the glutamatergic and endogenous opioidergic systems in the paradoxical pain evoked by the simultaneous application of innocuous warm and cold stimuli to the skin with a "thermal grill". Two parallel randomized, double-blind, cross-over studies, including two groups of 12 healthy volunteers, were carried out to compare the effects of i.v. ketamine or naloxone to those of placebo, on the sensations produced by a thermode (i.e. thermal grill) composed of six bars applied on the palmar surface of the right hand. The temperature of alternate (even- and odd-numbered) bars could be controlled independently by Peltier elements to produce various patterns of the grill. During each experimental session we measured the effects of ketamine, naloxone or placebo on the intensity of: (i) paradoxical pain; (ii) "normal" thermal (heat and cold) pain; and (iii) non-painful thermal (warm and cool) sensations. Ketamine administration resulted in a significant reduction of paradoxical pain intensity but did not alter normal pain or non-painful thermal sensations. By contrast, naloxone had no effect on paradoxical pain, normal pain or non-painful thermal sensations. This study demonstrates for the first time that the "thermal grill illusion of pain" can be modulated pharmacologically. This paradoxical pain, which involves the glutamatergic systems, acting through the NMDA receptors, but not the tonic endogenous opioids systems, might share some mechanisms with pathological pain.
Article
In this study untrained subjects were tested with warm + cold stimulation, using, in all, four different types of grills. The temperatures were 36°, 38°, 40°, 42°, 44°, 46°, 48°, and 50° C., compounded with 10°, 15°, 20° and 25° C. Direct or indirect comparison with the corresponding simple stimulation was made in each case. "Hot" was not reported in response to the compound stimulation, except in a very few cases. Generally, the intensity of the warmth reported with compound stimulation was less than that with corresponding simple stimulation. Earlier workers, using introspectively trained observers, found that "heat" was reported in response to such compound stimulation in a majority of cases. In explanation of the discrepancy, it is suggested that the "heat" of the trained observer is a different experience from the common experience "hot." Synthetic experiments with trained observers, therefore, should not be cited as evidence that the Alrutz theory applies to the common experience of "hot." (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
This study aimed to investigate the quality of the thermal grill illusion (TGI) and the importance of stimulus parameters (distance between, and number of stimulation bars). Twenty-one different stimuli were applied to a group of 19 healthy subjects on the glabrous skin over the palm and fingers. The TGI was found to be painful (19.42% on the palm; 17.98% on the fingers), mechanical (25.24% on the palm; 5.62% on the fingers), emotional (13.59% on the palm; 14.61% on the fingers) or unusual (42.72% on the palm; 61.8% on the fingers) sensations. A total of 89.5% (palm) and 94.4% (fingers) of the subjects reported TGI. Between 45% (fingers) and 50% (palm) of the stimuli elicited TGI. Neither the distance (2 approximately 10 mm) between adjacent warm (40 +/- 1 degrees C) and cold (20 +/- 1 degrees C) bars nor the number of the stimulation bars (2 approximately 6) significantly affected the occurrence of the TGI (N.S.). The average reaction time was 2.4 +/- 0.1 seconds to the TGI sensation. Females showed longer reaction time than males (P <or= 0.001). The distance and number of stimulation bars were not important to the sensation of TGI, of which the responses varied. These results are useful for future TGI studies with respect to experimental design. The variability of the TGI needs to be considered in future experimental and clinical studies.
Article
This study presents a German version of the McGill Pain Questionnaire (MPQ) developed by strict adherence to the methodology originally employed by Melzack and Torgerson. Three groups of subjects participated: The first group (n = 40) was used to construct a 5-point intensity scale. The second group (n = 42) was presented a preliminary translation of the MPQ and asked to assign an intensity rating out of the 5-point intensity scale to each of the 78 adjectives. In the last phase, adjectives whose mean ratings differed markedly from those in the original MPQ were resubmitted, along with 3-4 synonyms to a third group (n = 40) who was again asked to assign an intensity value to each word. Finally, the adjectives whose ratings corresponded closest, and thus resulted in congruent rank positions to those of the English originals, were selected. The present counterpart to the MPQ retains the original grouping of adjectives, the identical number of words per group as well as their rank positions within groups. Thus a comparison between German and English mean ratings, rank values and number of words chosen as well as statistical calculations derived therefrom is feasible.
Article
In Thunberg's thermal grill illusion, first demonstrated in 1896, a sensation of strong, often painful heat is elicited by touching interlaced warm and cool bars to the skin. Neurophysiological recordings from two classes of ascending spinothalamic tract neurons that are sensitive to innocuous or noxious cold showed differential responses to the grill. On the basis of these results, a simple model of central disinhibition, or unmasking, predicted a quantitative correspondence between grill-evoked pain and cold-evoked pain, which was verified psychophysically. This integration of pain and temperature can explain the thermal grill illusion and the burning sensation of cold pain and may also provide a basis for the cold-evoked, burning pain of the classic thalamic pain syndrome.
Article
Touching warm and cool bars that are spatially interlaced produces a painful burning sensation resembling that caused by intense, noxious cold. We demonstrated previously that this thermal grill illusion can be explained as an unmasking phenomenon that reveals the central inhibition of pain by thermosensory integration. In order to localize this unmasking in the human brain, we have used positron emission tomography (PET) to compare the cortical activation patterns evoked by the thermal grill and by cool, warm, noxious cold and noxious heat stimuli. The thermal grill illusion produces activation in the anterior cingulate cortex, whereas its component warm and cool stimuli do not. This area is also activated by noxious heat or cold. Thus, increased activity in the anterior cingulate cortex appears to be selectively associated with the perception of thermal pain. Disruption of thermosensory and pain integration may account for the central pain syndrome that can occur after stroke damage.
Article
A paradoxical painful sensation can be elicited by the simultaneous application of innocuous warm and cold stimuli to the skin. In the present study, we analyzed the conditions of production of this unique experimental illusion of pain in 52 healthy volunteers (27 men, 25 women). The stimuli were produced by a thermode composed of six bars whose temperature was controlled by Peltier elements. The temperature of alternate (even- and odd-numbered) bars could be controlled independently to produce various patterns of the 'thermal grill'. After measuring the cold and heat pain thresholds, a series of combinations of warm and cold stimuli, whose distance to the thermal pain threshold was at least 4 degrees C, were applied on the palmar surface of the right hand during 30s. After each stimulus, the subjects had to describe and rate their sensations on visual analog scales. Paradoxical painful sensations, mostly described as burning, were reported by all the subjects but three. However, the phenomenon was less frequent in approximately one third of ('low responder') volunteers. The frequency and intensity of such painful sensations were directly related to the magnitude (i.e. 5-25 degrees C) of the difference of the temperature between the warm and cold bars of the grill. The combination of increasingly colder temperature to a given warm temperature induces similar effects as combining increasingly warmer temperature to a given cold temperature. These results suggest that pain can be the result of a simple addition of non-noxious warm and cold signals.
Article
Concurrent applications to the skin of spatially adjacent bands of innocuous warm and cool stimuli would elicit a peculiar sensation, known as the 'thermal grill illusion'. To validate the thermal grill as a research tool, this two-phase study qualitatively characterizes this peculiar sensation and further quantitatively establishes the temperature matching of the most intense/noxious thermal grill stimulations at two different time points. The temperature combinations (degrees C) tested were: 18/18, 42/42, 18/42, 20/20, 40/40, 20/40, 22/22, 38/38, 22/38, 24/24, 36/36 and 24/36. None of the subjects reported pain with single temperature combinations. However, hot associated with pain and burning sensations were reported in all mixed temperature combinations tested. The VAS scores for pain were significantly elevated for 20/40 and 18/42 in comparison to 22/38 and 24/36 (P<0.007). At the 3-second time point, the matching temperatures (+/-SD) of 20/40 and 18/42 were 45.7+/-1.8 (range 44-48) and 46.6+/-1.5 (range 44-48) degrees C, respectively, whereas the matching temperatures for the single temperature combinations were similar to the set temperatures. Importantly, at the 10-second time point, none of the combinations were significantly greater than the highest of the pair of stimuli. The time course variation in the perception of the combined stimuli suggests an adaptation occurred in central processing.
Article
It was recently found that nociceptive sensations (stinging, pricking, or burning) can be evoked by cooling or heating the skin to innocuous temperatures (e.g., 29 and 37 degrees C). Here, we show that this low-threshold thermal nociception (LTN) can be traced to sensitive 'spots' in the skin equivalent to classically defined warm spots and cold spots. Because earlier work had shown that LTN is inhibited by simply touching a thermode to the skin, a spatial search procedure was devised that minimized tactile stimulation by sliding small thermodes (16 and 1mm(2)) set to 28 or 36 degrees C slowly across the lubricated skin of the forearm. The procedure uncovered three types of temperature-sensitive sites (thermal, bimodal, and nociceptive) that contained one or more thermal, nociceptive, or (rarely) bimodal spots. Repeated testing indicated that bimodal and nociceptive sites were less stable over time than thermal sites, and that mechanical contact differentially inhibited nociceptive sensations. Intensity ratings collected over a range of temperatures showed that LTN increased monotonically on heat-sensitive sites but not on cold-sensitive sites. These results provide psychophysical evidence that stimulation from primary afferent fibers with thresholds in the range of warm fibers and cold fibers is relayed to the pain pathway. However, the labile nature of LTN implies that these low-threshold nociceptive inputs are subject to inhibitory controls. The implications of these findings for the roles of putative temperature receptors and nociceptors in innocuous thermoreception and thermal pain are discussed.
Nociception and pain in thermal skin sensitivity
  • D Kleinböhl
  • J Trojan
  • R Hölzl
D. Kleinböhl, J. Trojan, R. Hölzl, Nociception and pain in thermal skin sensitivity, in: B. Berglund, G.B. Rossi, J. Townsend, L. Pendrill (Eds.), Measurements with Persons: Theory and Methods. Part II: Implementation Areas (Chapter 12), Taylor & Francis, London, New York, 2011.
The thermal grill illusion: unmasking the burn of cold pain
  • A D Craig
  • M C Bushnell
A.D. Craig, M.C. Bushnell, The thermal grill illusion: unmasking the burn of cold pain, Science 265 (1994) 252-255.
  • N C Burnett
  • K M Dallenbach
  • Heat Intensity
N.C. Burnett, K.M. Dallenbach, Heat Intensity, Am. J. Psychol. 40 (1928) 484-494.