Relationship between subjective pain estimation and somatosensory evoked potentials by electrical tooth stimulation

The relationship between the amplitude of somatosensory evoked potentials (SEP) and the subjective pain estimation using a visual analogue scale (VAS) was examined in 8 volunteers undergoing randomized electrical tooth stimulation with 3 different intensities. Randomized stimulation was used instead of repetitive stimulation with a fixed intensity in order to minimize the phenomena of habituation and expectancy in recording the SEP and VAS. The VAS scores increased significantly with the stimulus intensity. The amplitude with a latency between 160 and 300 msec (N160-P300) showed a significant increase with the increased intensity. But the amplitudes between 60 and 110 msec (N60-P110) and between 110 and 160 msec (P110-N160) showed no significant change. There was a significant correlation between the amplitude of N160-P300 and the VAS scores. These findings indicate that the component between 160 and 300 msec reflects the perceived pain intensity and the psychological evaluation processes such as cognition, meaning, interpretation and appreciation of pain. The method of randomized stimulation can serve as a simple and useful way for the objective or subjective pain estimation.