EFFECT OF TRANSCUTANEOUS ELECTRICAL NERVE-STIMULATION (TENS) ON CENTRAL-NERVOUS-SYSTEM AMPLIFICATION OF SOMATOSENSORY INPUT

The effect of transcutaneous electrical nerve stimulation (TENS) on th e central nervous system amplification process was investigated focusi ng on the dorsal column-medial lemniscal pathway, because the dorsal c olumn nucleus was recently shown to receive multiple sources of sensor y information, including pain. Short latency somatosensory evoked pote ntials (SSEPs) were recorded in ten healthy normal volunteers, Amplitu de changes in each SSEP component (the N9 brachial plexus potential, t he P14 potential that originates from the cervicomedullary junction, s pinal N13/P13 generated by the cervical dorsal horn and the cortical N 20/P25 potential) were studied at stimulus strenghts ranging from the threshold (40% maximum stimulus) to 2.5 times the threshold (maximum). The findings suggest that sensory amplification begins at the P14 gen erator source near the cuneate nucleus. There was no statistically sig nificant difference in sensory amplification between P14 and cortical N20/P25, indicating that the cuneate nucleus is the main site of the c entral amplifying process. When TENS was applied to the palm distal to the median nerve stimulation used for SSEP, cortical N20/P25 amplific ation disappeared, evidence that TENS suppresses the central amplifica tion phenomenon, most probably at the level of the cuneate nucleus.