Effects of operantly conditioning the amplitude of the P200 peak of the SEP on pain sensitivity and the spinal nociceptive withdrawal reflex in humans.

This study attempted to replicate and extend earlier work that reported that the amplitude of the P200 peak of the human somatosensory evoked potential (SEP) can be increased and decreased when reward is made contingent upon change and that these changes are accompanied by alterations in pain sensitivity. Twenty-one subjects were able to make the amplitude of the P200 peak evoked by sural nerve stimulation larger during increased training (up-training) than during decreased training (down-training). There were no differences in the sural nerve compound action potential between up-training and down-training. This finding demonstrates that the change in P200 amplitude was not due to a change in stimulus efficacy, but rather to a change within the central nervous system. Subjective pain ratings and a nociceptive spinal reflex were the same in up-training as in down-training. Thus, conditioned changes in P200 amplitude do not alter pain sensitivity.