Effects of Passive Finger Movement on Cortical Excitability

This study examined the effects of joint angle and passive movement direction on corticospinal excitability. The subjects were 14 healthy adults from whom consent could be obtained. We performed two experiments. In Experiment 1, we measured motor evoked potential (MEP) amplitude, F-wave and M-wave at 0° and 20° adduction during adduction or abduction movement, in the range of movement from 10° abduction to 30° adduction. In Experiment 2, MEPs were measured at static 0° and 20° adduction during passive adduction from 10° adduction to 30° adduction and static 20° adduction. MEP, F-waves and M-waves were recorded from the right first dorsal interosseous (FDI) muscle. Experiment 1 revealed significantly increased MEP amplitude at 0° during passive adduction compared to static 0° (p < 0.01). No other significant differences in MEP, M-wave and F-wave parameters were observed. In Experiment 2, MEP amplitude was significantly higher at 20° adduction during passive adduction compared with static 0° (p < 0.01). Based on these findings, it appears that fluctuations in MEP amplitude values during passive movement are not influenced by joint angle, but rather it is possible that it is due to intracortical afferent facilitation (AF) dependent on afferent input due to the start of movement and interstimulus interval (ISI) of transcranial magnetic stimulation (TMS).