Gating of the early components of the frontal and parietal somatosensory evoked potentials in different sensory-motor interference modalities.

Three different interfering conditions were studied during the recording of pre- and postcentral somatosensory evoked potentials (SEPs) following median nerve stimulation at the wrist in 16 normal subjects: active finger movement (MVT), light superficial massage (LSM) and deep muscular massage (DMM) of the hand. Special attention was focused on selective effects on individual SEP components. The frontal N30 component showed the most significant amplitude reduction during the three interfering conditions (76.4% of reduction in MVT, 36.4% in DMM and 32.9% in LSM). In contrast the frontal N23 was not significantly changed and the preceding P22 component was only reduced in the MVT condition. Postcentral N20 was unchanged by the three conditions while P27 was clearly gated by movement but not significantly by LSM and DMM. The three interfering conditions enhanced the parietal N32 and had no significant effect on the parietal P45. An important point was the interindividual variability of these effects and it appeared that group average wave forms would therefore be confusing. The peak latency of some SEP components was changed during the interfering conditions. The most important effect was an increase of postcentral P45 latency which was found to be related to the amplitude enhancement of N32.