Excitability changes in the ipsilateral primary motor cortex during rhythmic contraction of finger muscles.
The aim of this study was to determine whether the excitatory ipsilateral primary motor cortex (ipsi-M1) is affected by changes in the frequency of rhythmic voluntary contraction of the left first dorsal interosseous (FDI) induced by repetitive abduction of the left index-finger. Transcranial magnetic stimulations were delivered to the left M1 during repetitive left index-finger abduction at 1, 2, and 3Hz, and motor evoked potentials (MEPs) were simultaneously evoked in the resting right (Rt)-FDI, Rt-abductor pollicis brevis, and Rt-abductor digiti minimi. The stimulus-response (S-R) curve of the MEP at each frequency was recorded. In addition, F-waves were recorded from the Rt-FDI during these rhythmic contraction tasks in order to examine the changes in spinal motoneuron excitability. MEPs were markedly increased under the 3Hz conditions compared with the other conditions. However, F-waves were hardly changed under these conditions. The S-R curve of the MEP induced under the 3Hz conditions was significantly steeper than the curves produced under other conditions. Our results indicate that the excitability of ipsi-M1 is affected by the frequency of rhythmic voluntary contraction of unilateral finger movement, which may be caused by neural inputs delivered via a transcallosal pathway.
Human Motor Control Laboratory, Division of Human Sciences, Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima 739-8521, Japan.
Kazumasa
K
Uehara
Takuya
T
Morishita
Kozo
K
Funase
D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D005385:Fingers / Q000294:innervation*; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010507:Periodicity; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult