Differences in nociception during voluntary flexion and extension.
The volar surface of the second toe on the right leg of 14 human subjects was stimulated with 10 msec electrical shocks at 1 Hz. Stimulus intensity was sufficient to evoke first and second pain and was kept constant throughout each trial. The right leg was held in a relaxed, flexed, or extended position for 10 shocks and was then moved to and held at another of the positions for another 10 shocks. Subjects were asked to report if the intensity of the stimulus remained constant, increased or decreased after moving to the second position in each trial. Several statistical analyses showed a significant (P = 0.04 to less than 0.001) trend for the perceived pain to be more intense when the leg was held in the flexed position than when in the extended position. The results support a hypothesis that populations of neurons may contribute simultaneously to sensory perception and segmental reflex responses evoked by noxious stimuli as well as to voluntary motor behavior.
D000328:Adult; D006801:Humans; D007866:Leg; D009068:Movement; D009474:Neurons / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D010147:Pain Measurement; D012018:Reflex / Q000502:physiology; D012684:Sensory Thresholds