Department of Neurosurgery, Saitama Medical University, Saitama, Japan.
Restor Neurol Neurosci. 2010;28(4):437-48. doi: 10.3233/RNN-2010-0562.
Disruption of a cortical region can paradoxically improve behavior. After unilateral damage to the primary motor cortex (M1), increased excitability of the unaffected M1 has been shown. The M1 plays a critical role in motor performance and also early aspects of motor skill learning. Repetitive transcranial magnetic stimulation (rTMS) of one motor cortex can lead a temporary reduction in cortical excitability. We hypothesize that unilateral suppression of one M1 by rTMS may increase excitability of the unaffected motor cortex and thus improve motor performance and motor skill learning with the ipsilateral hand by releasing the contralateral motor cortex from transcallosal inhibition.
Forty healthy volunteers participated in our study; 16 for the experiment I and 24 for the experiment II. In the experiment I, after practicing a sequential simple key-pressing task with the index finger, their motor performance was monitored before and after slow-frequency (1Hz) rTMS, applied on the M1 ipsilateral or contralateral to the hand, ipsilateral premotor area or vertex (Cz). In the experiment II, participants were randomly divided into three stimulation groups: i) ipsilateral M1; ii) contralateral M1; and iii) Cz. rTMS was applied before the initiation of practice and learning of a simple motor skill. Mean execution time and error rate were recorded in 4 sessions distributed over 2 days.
In experiment I: rTMS of M1 shortened execution time of the motor task with the ipsilateral hand, without affecting performance with the contralateral hand. This effect outlasted rTMS by at least 10 min, and was most prominent for M1 stimulation. In experiment II, disruption of M1 with rTMS slowed down skill acquisition with the contralateral hand, but paradoxically accelerated learning with the ipsilateral hand. This effect was evident during the first of 2 days of practice in the group with rTMS over the ipsilateral M1 compared to the other two groups (Cz and contralateral M1).
Our results support the notion of an interhemispheric competition, and demonstrate the utility of rTMS to explore the functional facilitation of the un-stimulated counterpart M1 with effects on motor execution and learning, which may have implications for neurorehabilitation.
皮质区域的破坏反而可以改善行为。单侧初级运动皮层（M1）损伤后，观察到未受影响的 M1 的兴奋性增加。M1 在运动表现中起着关键作用，并且在运动技能学习的早期阶段也起着关键作用。经颅磁刺激（rTMS）单侧刺激一个运动皮层会导致皮质兴奋性暂时降低。我们假设通过 rTMS 单侧抑制一个 M1 可能会增加未受影响的运动皮层的兴奋性，从而通过释放来自对侧皮质的跨皮质抑制来改善同侧手的运动表现和运动技能学习。
40 名健康志愿者参与了我们的研究；16 名用于实验 I，24 名用于实验 II。在实验 I 中，在使用食指练习顺序简单按键任务后，在低频（1Hz）rTMS 刺激 M1 同侧或对侧、同侧运动前区或顶点（Cz）之前和之后监测他们的运动表现。在实验 II 中，参与者被随机分为三组刺激组：i）同侧 M1；ii）对侧 M1；iii）Cz。rTMS 在开始练习和学习简单运动技能之前应用。在 2 天的 4 个会话中记录平均执行时间和错误率。
在实验 I 中：M1 的 rTMS 缩短了同侧手运动任务的执行时间，而不影响对侧手的表现。这种影响至少持续了 10 分钟，并且在 M1 刺激时最为明显。在实验 II 中，rTMS 破坏 M1 会减缓对侧手技能的获得，但相反会加速同侧手的学习。与其他两组（Cz 和对侧 M1）相比，在第一天练习中，rTMS 组中同侧 M1 的刺激明显加速了学习。
我们的结果支持了大脑半球间竞争的概念，并证明了 rTMS 可用于探索对未刺激的对侧 M1 的功能促进作用，这可能对神经康复有意义。
