Operant conditioning of trigeminally-evoked cortical potentials: correlated effects on facial nociception

The effects of operant conditioning somatosensory evoked potential (SEP) amplitude on nociceptive sensitivity were studied in albino rats. SEPs were evoked by stimulation to the descending trigeminal tract. Rewarding medial forebrain bundle stimulation (at intensities predetermined to sustain bar pressing) was made contingent upon the animal making the amplitude of the SEP 0.5 standard deviation (S.D.) large (uptraining) or 0.5 S.D. smaller (downtraining) than the predetermined mean value. Nociceptive sensitivity was measured immediately following the conditioning session by heating the rat's face and noting the latency of a defensive face rubbing response directed at that area of the face. Increasing the amplitude of the SEP (uptraining) was associated with a decrease in noxious sensitivity. Decreasing the amplitude of the SEP (downtraining) was associated with an increase in noxious sensitivity.