Effects of body location on the thermal grill illusion of pain
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1
University of Toronto, Department of Physiology, Canada
The simultaneous application of interlaced warm (40°C) and cool (20°C) temperature bars (a thermal grill, TG) is known to elicit paradoxical pain when applied to the hand or forearm (termed the thermal grill illusion, TGI). In a previous study, we found that participants experienced more pain and unpleasantness when the TG is applied to the palm vs. the forearm. There have been no further reports on whether a TGI can be elicited from other body sites. In this study, we extended the testing of this phenomenon to the back, calf, and foot. Thermal stimuli were produced by a 1x6 matrix of Peltier-controlled thermodes. Three bar configurations were tested: all bars 40°C (warm), all bars 20ºC, and alternating bars 20°C/40°C (TG) at four sites: palm, back, calf, and plantar surface of the foot. Stimulus duration was 60s. Two runs were conducted for each condition at every location. Presentation of stimuli was pseudo-randomized by location and condition. After completion of each run, subjects rated pain intensity and unpleasantness on an 11 point numeric rating scale (0 - 10). Ratings obtained at the four locations were compared for each bar configuration (repeated-measures ANOVA). In agreement with previous studies describing a 20-30% of “non-responders” amongst their sample, two of the 19 subjects that partook in this study did not perceive pain in response to the TG at any of the four locations, and were excluded from subsequent analyses. Amongst the remaining participants, the TGI was not necessarily elicited from all body areas. Pain and unpleasantness ratings elicited during the TG condition across all runs were significantly higher than when the bars were all warm or all cool (p<0.001, for all comparisons). The main effect of location was also significant (p<0.05 for pain, p<0.001 for unpleasantness). For the TG condition, the back and palm elicited the highest pain and unpleasantness ratings (3.3,± 0.6, and 4.3, ±0.6; and 3.3±0.8 and 3.9±0.7; respectively), followed by the calf (2.3±0.6 and 2.9±0.5), and foot (1.8±0.4 and 2.1±0.4). In conclusion, an illusion of pain in response to the TG can be evoked from all four body sites tested. Furthermore, there were significant differences in the magnitude of the TG across the body sites, possibly due to differences in peripheral innervation density and receptive field size and/or central processing.
Acknowledgement: CIHR CFC Grant 204681
Conference:
B.R.A.I.N. platform in Physiology poster day 2009, Toronto, ON, Canada, 16 Dec - 16 Dec, 2009.
Presentation Type:
Oral Presentation
Topic:
Oral presentations
Citation:
Brunello
ME,
Hunter
JP,
Popovic
M and
Dostrovsky
JO
(2009). Effects of body location on the thermal grill illusion of pain.
Front. Neurosci.
Conference Abstract:
B.R.A.I.N. platform in Physiology poster day 2009.
doi: 10.3389/conf.neuro.03.2009.17.005
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Received:
16 Dec 2009;
Published Online:
16 Dec 2009.
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Correspondence:
Maria E Brunello, University of Toronto, Department of Physiology, Toronto, Canada, me.brunello@gmail.com