P2-97. Different information processing in primary somatosensory area during force generation and relaxation.

We investigated the modulation of somatosensory evoked potentials (SEPs) during force generation and force relaxation in a visuomotor tracking task. The target force line moved up continuously from 0% to 20% of maximal voluntary contraction (MVC) (the force generation phase: FG phase) and moved down from 20% to 0% of MVC (the force relaxation phase: FR phase) in 7 s at a constant velocity. Subjects tracked a target line with a line, which represented their own force generated by grip movement with the right hand as accurately as possible during concurrent electrical stimulation. SEPs following stimulation of the median nerve were obtained in each phase. Compared with the stationary condition, the N30 at Fz and P27 at C3’ showed a significant reduction in amplitude in the FG and FR phases. Furthermore, those were significantly smaller in amplitude in the FG than FR phase. Previous studies reported that the strength of muscle force affects the SEP gating. Although the average amount of force exertion was the same in the both phases, our results showed the different modulation of SEP amplitude. These results indicated that sensorimotor integration in the primary somatosensory area was dependent on the context of movement exertion. [ABSTRACT FROM AUTHOR]