title: Relationships between the paradoxical painful and nonpainful sensations induced by a thermal grill.
abstract: 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 palms of the right hands of 21 volunteers with a thermode consisting of 6 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 2 paradoxical phenomena were reported for most of the series of stimuli (n=66). In each of these series, the 2 phenomena occurred 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 nonpainful paradoxical sensations evoked by the thermal grill that 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.
authors.affiliation: Inserm U-987, Centre d'Evaluation et de Traitement de la Douleur, CHU Ambroise Paré, Assistance Publique Hôpitaux de Paris, Boulogne-Billancourt, France Université Versailles-Saint-Quentin, Versailles, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Adam
authors.forename: Pascal
authors.initials: P
authors.lastname: Alfonsi
authors.forename: Delphine
authors.initials: D
authors.lastname: Kern
authors.forename: Didier
authors.initials: D
authors.lastname: Bouhassira
mesh_terms: D000328:Adult; D003080:Cold Temperature / Q000009:adverse effects; D004056:Differential Threshold / Q000502:physiology*; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology*; D013697:Thermosensing / Q000502:physiology*
keywords: Experimental model; Healthy volunteers; Psychophysics; Thermal sensation; Thermoreception