Transient decrease of sensory perception after thermoalgesic stimuli for quantitative sensory testing

Transient decrease in the excitability of a reflex circuit following its activation by appropriate stimuli is a well-recognized phenomenon, but it is unclear how this applies to thermoalgesic stimuli during quantitative sensory testing (QST). We examined the effects induced by a thermoalgesic (conditioning) stimulus on the response to a subsequent (test) stimulus of the same characteristics. All tests were done using a Peltier thermode with a surface area of 12.5 cm(2) using ramp rates of 2 degrees C/s and variable interstimulus intervals (ISIs) ranging from 10 to 60 s. Perception was measured with an electronic visual analog scale. No changes were observed in latency of pain perception. However, latency of warm perception was significantly delayed and pain perception intensity was significantly reduced with respect to conditioning stimuli at ISIs below 60 s. Our results indicate a transient saturation of warm and heat pain perception systems after a thermoalgesic stimulus. We therefore recommend that time intervals of >1 min be used between two consecutive thermoalgesic stimuli when examining QST.