Somatosensory evoked potentials modification related to isometric voluntary contraction.

Somatosensory evoked potentials were elicited by applying an electrical stimulus to the median nerve while the subjects performed a handgrip isometric contraction. Somatosensory evoked potentials (SEPs) were recorded from scalp positions C3 + 2 and C3-2. SEPs during the increase phase and decrease phase of force, and during the hold phase (period of maintenance of steady force) of isometric contraction were compared with potentials during rest. SEPs during the three phases of isometric contraction were also compared. Changes in SEP latencies were not observed. The increase or decrease phase of force and the hold phase caused suppression of the relatively late N55-P100 component when compared to rest. There was no difference in the amplitude of SEPs during the increase or decrease phase. During the hold phase the early N20-P30 component was increased when compared to the other two phases. The selective changes of SEPs during the three phases of isometric-anisotonic contraction suggested task dependence of the gating process.