Background

Motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) are typically recorded via surface electromyography (EMG). However, another suitable alternative may be recording torque output associated with MEPs, especially when studying multiheaded muscles (e.g. quadriceps) for which EMG may not be ideal.

Methods

We recorded the motor evoked torque elicited by TMS along with conventional EMG-based MEPs (MEP_EMG) over a range of TMS intensities (100-140% of active motor threshold [AMT]) from twenty healthy young adults on two different days. MEPs were normalized using different normalization procedures (raw, normalized to maximum voluntary isometric contraction [MVIC], and peak MEP). Additionally, motor evoked torque was normalized to TMS-evoked peripheral resting twitch torque. Intraclass correlation coefficients (ICCs) were determined for each of these variables to compute reliability.

Results

Motor evoked torque showed good to excellent reliability (ICC: 0.65-0.90) at TMS intensities ≥ 110% AMT, except when normalized by peak MEP. The reliability of raw MEP_EMG and MVIC normalized MEP_EMG was fair to excellent only at ≥ 130% AMT (ICC: 0.42-0.82) and at ≥ 120% AMT (ICC: 0.41-0.83), respectively. The reliability of both MEP_EMG and motor evoked torque generally increased with increasing TMS intensities, with motor evoked torque normalized to the resting twitch torque yielding the best ICC scores.

Comparison with existing methods

When compared with conventional MEP_EMG, motor evoked torque offers superior and reliable estimates of corticospinal excitability, particularly when normalized to resting twitch torque.

Conclusions

TMS-induced motor evoked torque can reliably be used to measure corticospinal excitability in the quadriceps muscles.

中文翻译：

---

使用诱发扭矩响应评估运动皮层兴奋性：一种具有高可靠性的新工具

背景

经颅磁刺激 (TMS) 引发的运动诱发电位 (MEP) 通常通过表面肌电图 (EMG) 记录。然而，另一种合适的替代方法可能是记录与 MEP 相关的扭矩输出，尤其是在研究EMG 可能不理想的多头肌肉（例如股四头肌）时。

方法

我们在两个不同的日子里记录了 20 名健康年轻人在一系列 TMS 强度（主动运动阈值 [AMT] 的 100-140%）范围内由 TMS 和传统的基于 EMG 的 MEP (MEP _{EMG ) 引发的运动诱发扭矩。}使用不同的标准化程序（原始、标准化为最大自主等长收缩 [MVIC] 和峰值 MEP）对 MEP 进行标准化。此外，将运动诱发扭矩标准化为 TMS 诱发的外周静息抽搐扭矩。为这些变量中的每一个确定组内相关系数 (ICC) 以计算可靠性。

结果

运动诱发扭矩在 TMS 强度 ≥ 110% AMT 时表现出良好至极好的可靠性（ICC：0.65-0.90），除非通过峰值 MEP 标准化。原始 MEP _EMG和 MVIC 归一化 MEP _EMG的可靠性分别仅在 ≥ 130% AMT (ICC: 0.42-0.82) 和 ≥ 120% AMT (ICC: 0.41-0.83) 时表现良好。MEP _EMG和电机诱发扭矩的可靠性通常随着 TMS 强度的增加而增加，电机诱发扭矩归一化为静息抽搐扭矩，从而产生最佳 ICC 分数。

与现有方法的比较

与传统的 MEP _EMG相比，运动诱发扭矩提供了对皮质脊髓兴奋性的卓越和可靠的估计，特别是当归一化为静息抽搐扭矩时。

结论

TMS 诱导的运动诱发扭矩可以可靠地用于测量股四头肌的皮质脊髓兴奋性。