The somatosensory evoked potential (SEP) is attenuated (gating) and the spinal motoneuron pool is facilitated before and during movement. However, the relationship between these changes has not been elucidated. In the present study, the SEP and the evoked electromyogram were simultaneously recorded during a discriminative reaction task in seven healthy subjects . Electrical stimulation applied to the posterior tibial nerve in the popliteal fossa was used as a response signal . The experimental

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... ondition were: 1) full relaxation and no response to either right or left stimulation (Control); 2) no response to right stimulation and quick contraction of right ankle with left stimulation (L-R); 3) no response to left stimulation and quick contraction of right ankle with right stimulation (R-R). Right and left legs were randomly stimulated under each condition . The H-response gains of the right leg with movement were significantly facilitated compared to the left leg without movement in L-R and R-R conditions. The results indicated that movement enhanced the motoneuron excitability regardless of sensory concentration . In the L-R condition, N 40 at Cz evoked by left operative stimulation that produced right leg movement was significantly increased . However, in the R-R condition, it was significantly attenuated when it was recorded by right operative stimulation that produced right leg movement. These results indicated that concentration on the operative stimulation enhanced the N 40 gain and it reflected the concentration on sensory information, but simultaneously induced the movement, and its gain was strongly controlled by the motor system.