Effect of transcranial magnetic stimulation on bimanual movements.
Transcranial magnetic stimulation (TMS) of the motor cortex can interrupt voluntary contralateral rhythmic limb movements. Using the method of "resetting index" (RI), our study investigated the TMS effect on different types of bimanual movements. Six normal subjects participated. For unimanual movement, each subject tapped either the right or left index finger at a comfortable rate. For bimanual movement, index fingers of both hands tapped in the same (in-phase) direction or in the opposite (antiphase) direction. TMS was applied to each hemisphere separately at various intensities from 0.5 to 1.5 times motor threshold (MT). TMS interruption of rhythm was quantified by RI. For the unimanual movements, TMS disrupted both contralateral and ipsilateral rhythmic hand movements, although the effect was much less in the ipsilateral hand. For the bimanual in-phase task, TMS could simultaneously reset the rhythmic movements of both hands, but the effect on the contralateral hand was less and the effect on the ipsilateral hand was more compared with the unimanual tasks. Similar effects were seen from right and left hemisphere stimulation. TMS had little effect on the bimanual antiphase task. The equal effect of right and left hemisphere stimulation indicates that neither motor cortex is dominant for simple bimanual in-phase movement. The smaller influence of contralateral stimulation and the greater effect of ipsilateral stimulation during bimanual in-phase movement compared with unimanual movement suggest hemispheric coupling. The antiphase movements were resistant to TMS disruption, and this suggests that control of rhythm differs in the 2 tasks. TMS produced a transient asynchrony of movements on the 2 sides, indicating that both motor cortices might be downstream of the clocking command or that the clocking is a consequence of the 2 hemispheres communicating equally with each other.
Chen
Jen-Tse
JT
Department of Neurology, the Neurological Institute, Taipei Veterans General Hospital, 201, Section II, Shih-Pai Rd., Pei-tou District, Taipei 11217, Taiwan.
Lin
Yung-Yang
YY
Shan
Din-E
DE
Wu
Zin-An
ZA
Hallett
Mark
M
Liao
Kwong-Kum
KK
D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology / Q000528:radiation effects; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006225:Hand / Q000502:physiology / Q000528:radiation effects; D006801:Humans; D008297:Male; D008954:Models, Biological; D009043:Motor Activity / Q000502:physiology / Q000528:radiation effects*; D009044:Motor Cortex / Q000528:radiation effects*; D011597:Psychomotor Performance / Q000502:physiology / Q000528:radiation effects*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation