An experimental system for a heterotopic pain stimulation study in humans.

So far heterotopic pain stimulation study has been performed in humans. Many studies have examined changes in subjective pain threshold and nociceptive somatic reflex. However, there are few studies using somatosensory evoked potentials (SEPs) for heterotopic pain stimulation study. Here we describe a new experimental system for a heterotopic pain stimulation study in humans. This system consists of three subsystems including the electrical test stimulation for teeth, the recording of SEP induced by electrical tooth stimulation and conditioning nerve stimulation. The preliminary experiment performed in eight healthy subjects indicated that the electrical test stimulation subsystem with the SEP recording subsystem is also very well indicated for subjective and objective pain evaluation, including VAS estimation and the amplitude of the SEP late component induced by electrical tooth stimulation. Under the experimental system in the present study, electrical median nerve stimulation as conditioning stimulation significantly decreased both the SEP amplitude induced by electrical tooth simulation and subjective pain expressed by the VAS. These results revealed that our experimental system works well and it is very suitable and useful for the study of the pain mechanism under heterotopic stimulation in humans.