Department of Kinesiology, McMaster University , Hamilton, Ontario , Canada.
J Neurophysiol. 2019 Jul 1;122(1):368-377. doi: 10.1152/jn.00030.2019. Epub 2019 May 22.
Interhemispheric inhibition (IHI) between motor cortexes is thought to suppress unwanted mirror movements during voluntary behaviors and can be assessed using paired-pulse transcranial magnetic stimulation (TMS). The magnitude of IHI may be related to the size of the cortical representation for a given muscle as a mechanism for facilitating unimanual control. To date, the relationship between IHI and cortical muscle representations remains unknown. Fifteen healthy, right-handed individuals participated in the present study. IHI was examined in the right first dorsal interosseous (FDI) muscle by delivering conditioning TMS to ipsilateral (right) primary motor cortex (M1) followed by a test TMS pulse to contralateral (left) M1. The size of the FDI representation in M1 was determined by delivering suprathreshold TMS over a 5 × 5-cm grid centered on the FDI motor hotspot of the left M1. Both IHI and cortical territory were obtained during three conditions: rest, contralateral (right) FDI contraction, and ipsilateral (left) FDI contraction. Results indicate a significant association between IHI and the size of the FDI representation only in the context of contraction and not when the FDI muscle was relaxed. Specifically, reduced IHI corresponded to larger cortical FDI representations during both contralateral and ipsilateral contraction. These data demonstrate that, for a muscle of the hand, the magnitude of IHI and the cortical territory are associated within the context of muscle contraction. This study provides evidence from noninvasive brain stimulation that communication between the motor cortexes of the two hemispheres plays a role in shaping the motor cortical map that outputs to a hand muscle during active contraction of that muscle. This relationship exists only when the hand muscle is contracted. The findings presented further our understanding of motor control during unilateral movement and may inform future research targeting clinical populations that exhibit impaired unilateral control.
大脑两半球间的抑制（IHI）被认为可以抑制自愿行为过程中出现的不想要的镜像运动，并可通过对侧脉冲经颅磁刺激（TMS）来评估。IHI 的幅度可能与特定肌肉的皮质代表区大小有关，作为促进单手控制的一种机制。迄今为止，IHI 与皮质肌肉代表区之间的关系尚不清楚。本研究纳入了 15 名健康的右利手个体。通过同侧（右侧）初级运动皮层（M1）给予刺激 TMS，然后对侧（左侧）M1 给予测试 TMS 脉冲，检查右侧第一背侧骨间肌（FDI）的 IHI。通过在左侧 M1 的 FDI 运动热点上方的 5×5cm 网格上给予超阈值 TMS，确定 M1 中 FDI 的代表区大小。在三种情况下获得 IHI 和皮质区域：休息、对侧（右侧）FDI 收缩和同侧（左侧）FDI 收缩。结果表明，只有在收缩时，IHI 与 FDI 代表区的大小之间才存在显著关联，而在 FDI 肌肉放松时则没有。具体来说，在对侧和同侧收缩期间，减少的 IHI 对应于更大的皮质 FDI 代表区。这些数据表明，对于手部肌肉，在肌肉收缩的情况下，IHI 的幅度和皮质区域与皮质 FDI 代表区的大小之间存在关联。这项研究提供了来自非侵入性脑刺激的证据，表明两个半球的运动皮层之间的通讯在塑造运动皮层图谱方面发挥作用，该图谱在主动收缩手部肌肉时输出到手部肌肉。这种关系仅在手部肌肉收缩时存在。研究结果进一步加深了我们对单侧运动期间运动控制的理解，可能为针对表现出单侧控制受损的临床人群的未来研究提供信息。
