キーボードでの単語入力課題が同側一次運動野の皮質内抑制機能に及ぼす影響 [in Japanese] Effects of word processing task on intracortical inhibition circuits in the ipsilateral primary motor cortex [in Japanese]
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本研究では手指運動課題が持つ目的の明確性の違いが同側一次運動野 (M1) 内の短潜時および長潜時皮質内抑制 (SICI, LICI) に及ぼす影響について検討した。10名の右利き健常被験者が右示指で机上でのタッピング, 机上に投影されたレーザーキーボードへの実単語または疑似単語の入力を行った。安静時および運動課題時に運動肢と同側M1への単発および2連発経頭蓋磁気刺激 (TMS) を行い, 左第一背側骨間筋より運動誘発電位 (MEP) を記録した。2連発TMSの刺激間隔は3 ms, 100 msとし, SICI, LICIをそれぞれ評価した。安静時, 疑似単語入力課題と比較し, 実単語入力課題遂行時にLICIが有意に減弱した。単発TMSによるMEP振幅およびSICIは条件間の差が認められなかった。本結果は, 実在する単語を想起し入力する目的の明確性が高い動作時には, 運動肢と同側M1におけるLICIの機能は減弱することが示唆された。
Previous studies on transcranial magnetic stimulation (TMS) demonstrated that excitability of the ipsilateral primary motor cortex (M1) increases during unilateral compared with pseudo goal-directed finger movement. However, it remains unclear whether unilateral goal-directed movement modulates short (SICI) and long (LICI) interval intracortical inhibition circuits in the ipsilateral M1. The aim of the present study was to investigate whether SICI and LICI in the ipsilateral M1 are affected by execution of unilateral goal-directed finger movement. Ten healthy right-handed subjects performed four finger tapping tasks with the right index finger. The tasks included the following: (1) maintaining the finger at rest, as a control; (2) self-paced simple tapping on the desk; (3) typing real words using a virtual laser keyboard; and (4) typing pseudo words. During each of the tasks, TMS was delivered to evoke a motor evoked potential (MEP) from the left first dorsal interosseous (FDI) muscle. The test stimulus (TS) intensity was adjusted to elicit an MEP of approximately 1 mV peak-to-peak amplitude in the left FDI. For paired-pulse TMS paradigms, the conditioning stimulus (CS) intensity was set to 80% of the resting motor threshold for SICI. To assess LICI, the intensity of CS was set identical to that of the TS. Interstimulus intervals (ISI) between both CS and TS were fixed at 3 and 100 ms for SICI and LICI, respectively. EMG activity in the right FDI was similar during all finger tapping tasks. At an ISI of 100 ms, MEPs were significantly increased during the real words typing task compared with both control conditions and the pseudo words typing task. However, with single pulse TMS and paired-pulses with an ISI of 3 ms, MEPs remained unchanged during all tasks. These results indicate that LICI was significantly decreased during the real words typing task. Previous TMS studies reported that LICI in the contralateral M1 decreases during precision grip compared with simple finger abduction. Therefore, our findings suggest that performing unilateral goal-directed movement decrease not only LICI in the contralateral M1, but also that of the ipsilateral M1 via the transcallosal pathway.
- Japanese Journal of Clinical Neurophysiology
Japanese Journal of Clinical Neurophysiology 43(2), 70-78, 2015
Japanese Society of Clinical Neurophysiology