Abstract
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.
Highlights
The ‘thermal grill illusion’ (TGI) is a unique cutaneous sensation of unpleasantness, induced through the application of interlacing warm and cool stimuli
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 TGI6,9,10
We considered the relationship between rating of unpleasantness and changes in contact heat evoked potentials (CHEPs) outcomes during thermal grill illusion” (TGI) conditioning
Summary
The ‘thermal grill illusion’ (TGI) is a unique cutaneous sensation of unpleasantness, induced through the application of interlacing warm and cool stimuli. 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 1896, Torsten Thunberg first described the paradoxical sensation of heat in response to interlaced warm and cool stimulation. Investigating the conditioning effects of afferent stimuli on responses to noxious input has generated a wealth of knowledge regarding endogenous pathways modulating pain. The objective of the current study was to address the heterotopic conditioning effect of an unpleasant somatosensory afferent stimulus (i.e., interlaced hot and cool bars) on responses to noxious contact heat stimulation. To explore changes in cortical activity, the conditioning effect of the TGI was examined using contact heat evoked potentials (CHEPs)
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