Differential effects of muscle contraction from various body parts on neuromagnetic somatosensory responses

We studied eight healthy subjects with a whole-scalp 306-channel neuromagne tometer to explore the effect of motor activity from different body parts o n somato-sensory responses to left median nerve stimulation. The stimuli pr oduced clear tactile sensation without any motor movement. In the rest cond ition, the subject had no task. During contraction conditions, the subject had to maintain submaximal isometric contraction in masseter, left deltoid, left thenar, or left tibialis muscles. Short-latency responses from the pr imary somatosensory cortex did not change during contraction. Responses fro m both the right (contralateral) and left second somatosensory cortices (SI I) were significantly enhanced during contraction of the left thenar muscle s. Responses from the left SII were significantly enhanced also during cont raction of the left deltoid muscles, but they were decreased during contrac tion of the masseter and left tibialis anterior muscles. This study implies that SII: activation is modulated by motor activity and that the effect de pends on the topographical proximity of the stimulated and contracted body parts, (C) 2000 Academic Press.