Comparison of Corticospinal Excitability between Observations of Tonic Contraction and Rhythmic Movement: a TMS Study

Abstract

Two different experiments utilizing the motor imagery of nger movement were conducted. We attempted to reveal the difference in corticospinal excitability between tonic contraction (TC) and rhythmic movement (RM) by transcranial magnetic stimulation (TMS). The magnetic coil was placed over the subject s primary motor cortex to elicit motor-evoked potentials (MEPs) by TMS. We have previously shown that the MEP amplitude is modulated by the frequency of active and passive nger movements. We hypothesized that visual feedback affects the corticospinal excitability. In the present study, the subject observed both TCs and RMs, and the MEP amplitudes elicited by TMS during both tasks were analyzed to assess changes in corticospinal excitability in uenced by the motor imagery. A mirror box was used to show the subject the nger movement executed by a third person as if it were his own nger movement. For the TC task, the third person performed a pinching task consisting of TC of the index nger and thumb. The subject received visual feedback of the TC in the mirror. For the RM task, the subject observed the mirror while the third person performed RM of the index nger until TMS was applied. The frequencies of nger movement were 0.5, 1, 2, 3, and 4 Hz. The resulting MEP amplitudes for the RM task at movement frequencies of 2, 3, and 4 Hz were signi cantly lower than that for the TC task. These results indicate that corticospinal excitability is increased by visual feedback of TC but is modulated by that of RM.