The purpose of this study was to further develop methods to assess corticospinal divergence and muscle coupling using transcranial magnetic stimulation (TMS). Ten healthy right-handed adults participated (7 females, age 34.0 ± 12.9 years). Monophasic single pulses were delivered to 14 sites over the right primary motor cortex at 40, 60, 80 and 100% of maximum stimulator output (MSO), using MRI-based neuronavigation. Motor evoked potentials (MEPs) were recorded simultaneously from 9 muscles of the contralateral hand, wrist and arm. For each intensity, corticospinal divergence was quantified by the average number of muscles that responded to TMS per cortical site, coactivation across muscle pairs as reflected by overlap of cortical representations, and correlation of MEP amplitudes across muscle pairs. TMS to each muscle’s most responsive site elicited submaximal MEPs in most other muscles. The number of responsive muscles per cortical site and the extent of coactivation increased with increasing intensity (ANOVA, p < 0.001). In contrast, correlations of MEP amplitudes did not differ across the 60, 80 and 100% MSO intensities (ANOVA, p = 0.34), but did differ across muscle pairs (ANOVA, p < 0.001). Post hoc analysis identified 4 sets of muscle pairs (Tukey homogenous subsets, p < 0.05). Correlations were highest for pairs involving two hand muscles and lowest for pairs that included an upper arm muscle. Correlation of MEP amplitudes may quantify varying levels of muscle coupling. In future studies, this approach may be a biomarker to reveal altered coupling induced by neural injury, neural repair and/or motor learning.

本研究的目的是进一步开发使用经颅磁刺激 (TMS) 评估皮质脊髓发散和肌肉耦合的方法。10 名健康的右利手成年人参与（7 名女性，年龄 34.0 ± 12.9 岁）。使用基于 MRI 的神经导航，在最大刺激器输出 (MSO) 的 40、60、80 和 100% 处将单相单脉冲传送到右侧初级运动皮层的 14 个部位。同时记录对侧手、手腕和手臂的 9 块肌肉的运动诱发电位 (MEP)。对于每个强度，皮质脊髓发散通过每个皮质部位对 TMS 有反应的平均肌肉数量、皮质表示重叠所反映的肌肉对之间的共激活以及肌肉对之间 MEP 幅度的相关性来量化。TMS 对每块肌肉反应最灵敏的部位在大多数其他肌肉中引发次最大 MEP。每个皮质部位的反应性肌肉数量和共激活程度随着强度的增加而增加（ANOVA，p < 0.001）。相比之下，MEP 幅度的相关性在 60、80 和 100% MSO 强度之间没有差异（ANOVA，p = 0.34），但在肌肉对之间确实存在差异（ANOVA，p < 0.001）。事后分析确定了 4 组肌肉对（Tukey 同质子集，p < 0.05）。涉及两只手部肌肉的对相关性最高，而包括上臂肌肉的对相关性最低。MEP 幅度的相关性可以量化不同水平的肌肉耦合。在未来的研究中，这种方法可能是一种生物标志物，可以揭示由神经损伤、神经修复和/或运动学习引起的耦合改变。