Sensitization and habituation of AMH and C-fiber related percepts of repetitive radiant heat stimulation

Objective Pain perception involves neuronal plasticity at peripheral and central stages, resulting in sensitization or habituation, depending on intensity and temporal features of stimulation. Concurrent assessment of perceptual change over different time spans is therefore important for understanding the dynamics of pain processing. Methods A new psychophysical procedure was established to assess sensitization and habituation during repetitive radiant heat stimulation. Short-term perceptual change (<1 min) during trials with 10 stimuli applied at 3 frequencies (0.2–0.6–1.8 Hz) and 3 intensities was assessed for AMH-II or C-fiber related percepts. Perceptual changes were monitored for medium-term (1–15 min) and for long-term (15–90 min) time spans. Results Short-term sensitization occurred only at frequencies above 0.3 Hz and was affected by both stimulus frequency and intensity, but the AMH-fiber related sensitization depended on intensity only above 0.6 Hz. Multiple stimulation of the same skin area during medium-term time spans resulted in habituation. No long-term perceptual changes occurred. Conclusions The procedure permits concurrent assessment of short-term sensitization and medium-term habituation, assumed to be related to spinal windup and cutaneous nociceptive fiber fatigue, respectively. Significance The method is suitable for quantitative sensory testing of dynamic pain processing over different time spans, relevant in clinical testing of pain and in drug assessment.