• Charles J Vierck, Andre P Mauderli, and Joseph L Riley.
• Department of Neuroscience, College of Medicine, University of Florida, Gainesville, FL 32610-0244, USA. vierck@mbi.ufl.edu
• Exp Brain Res. 2013 Mar 1; 225 (3): 339-48.

AbstractRamp-and-hold heat stimulation with a Peltier thermode is a standard procedure for quantitative sensory testing of human pain sensitivity. Because myelinated and unmyelinated nociceptive afferents respond preferentially to changing and steady temperatures, respectively, ramp-and-hold heat stimulation could assess processing of input from A-delta nociceptors early and C nociceptors late during prolonged thermal stimulation. In order to evaluate the progression from dynamic change to a steady temperature during prolonged Peltier stimulation, recordings of temperatures at the probe-skin interface were obtained. First, recordings of temperature during contact-and-hold stimulation (solenoid powered delivery of a preheated thermode to the skin) provided an evaluation of heat dissipation from the beginning of stimulation, uncontaminated by ramping. The heat-sink effect lasted up to 8 s and accounted in part for a slow increase in pain intensity for stimulus durations of 1-16 s and stimulus intensities of 43-59 °C. Recordings during longer periods of stimulation showed that feedback-controlled Peltier stimulation generated oscillations in temperature that were tracked for up to 75 s by subjects' continuous ratings of pain. During 120-s trials, sensitization of pain was observed over 45 s after the oscillations subsided. Thus, long-duration stimulation can be utilized to evaluate sensitization, presumably of C nociception, when not disrupted by oscillations in thermode temperature (e.g., those inherent to feedback control of Peltier stimulation). In contrast, sensitization was not observed during 130.5 s of stimulation with alternately increasing and decreasing temperatures that repeatedly activated A-delta nociceptors.

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