Study on Corticospinal Excitability during Passive Symmetry and Asymmetry Finger Movements by TMS

Abstract

Bilateral information in primary motor cortices of human cerebral hemispheres is needed to produce simultaneous bilateral limb movement. The corpus callosum connecting homologous areas of cortex between the hemispheres is an important area to exert bilateral finger movements. It is unclear that the movement state of both fingers influences corticospinal excitability involving in contralateral movement. We measured corticospinal excitability during passive movement of both fingers using transcranial magnetic stimulation (TMS) on the primary motor cortex. The subjects performed passive movement of fingers using servomotors. TMS was applied at the two movement states of maximum flexion and extension position on metacarpophalangeal joint (MP joint) of dominant index finger, respectively. There were three kinds of movement task of symmetry, asymmetry and one-finger movements in this experiment. In one-finger movement task, the highest motor evoked potential (MEP) in electromyogram was measured with TMS timing of maximum extension of MP joint angle. Moreover, MEP with maximum extension of MP joint was lowest in symmetry movement task, but the MEP was conversely lowest with maximum flexion in asymmetry movement task. These results suggested that MEP depended on MP joint angle and the corticospinal excitability was inhibited when contralateral MP joint angle was with maximum extension.