Introduction

Previous research with transcranial magnetic stimulation (TMS) indicates that coil orientation (TMS current direction) and muscle activation state (rest or active) modify corticospinal and intracortical excitability of upper limb muscles. However, the extent to which these factors influence corticospinal and intracortical excitability of lower limb muscles is unknown. This study aimed to examine how variations in coil orientation and muscle activation affect corticospinal and intracortical excitability of tibialis anterior (TA), a lower leg muscle.

Methods

In 21 young (21.6 ± 3.3 years, 11 female) adults, TMS was administered to the motor cortical representation of TA in posterior-anterior (PA) and mediolateral (ML) orientations at rest and during muscle activation. Single-pulse TMS measures of motor evoked potential amplitude, in addition to resting and active motor thresholds, were used to index corticospinal excitability, whereas paired-pulse TMS measures of short-interval intracortical inhibition (SICI) and facilitation (SICF), and long-interval intracortical inhibition (LICI), were used to assess excitability of intracortical circuits.

Results

For single-pulse TMS, motor thresholds and test TMS intensity were lower for ML stimulation (all P < 0.05). In a resting muscle, ML TMS produced greater SICI (P < 0.001) and less SICF (both P < 0.05) when compared with PA TMS. In contrast, ML TMS in an active muscle resulted in reduced SICI but increased SICF (both P ≤ 0.001) when compared with PA TMS.

Conclusion

TMS coil orientation and muscle activation influence measurements of intracortical excitability recorded in the tibialis anterior, and are therefore important considerations in TMS studies of lower limb muscles.

中文翻译：

---

TMS 线圈方向和肌肉激活影响下肢皮质内兴奋性。

介绍

先前的经颅磁刺激 (TMS) 研究表明，线圈方向（TMS 电流方向）和肌肉激活状态（休息或活动）会改变上肢肌肉的皮质脊髓和皮质内兴奋性。然而，这些因素在多大程度上影响下肢肌肉的皮质脊髓和皮质内兴奋性尚不清楚。本研究旨在检查线圈方向和肌肉激活的变化如何影响小腿肌肉胫骨前肌 (TA) 的皮质脊髓和皮质内兴奋性。

方法

在 21 名年轻（​​21.6 ± 3.3 岁，11 名女性）成年人中，在休息和肌肉激活期间，TMS 在后-前 (PA) 和中外侧 (ML) 方向的运动皮层表示中被施用 TMS。除了静息和活动运动阈值外，运动诱发电位振幅的单脉冲 TMS 测量值还用于指示皮质脊髓兴奋性，而双脉冲 TMS 测量短间隔皮质内抑制 (SICI) 和易化 (SICF)，以及长-间隔皮质内抑制（LICI）用于评估皮质内回路的兴奋性。

结果

对于单脉冲 TMS，ML 刺激的运动阈值和测试 TMS 强度较低（所有 P < 0.05）。在静息肌肉中，与 PA TMS 相比，ML TMS 产生更大的 SICI（P < 0.001）和更少的 SICF（均 P < 0.05）。相比之下，与 PA TMS 相比，活动肌肉中的 ML TMS 导致 SICI 降低但 SICF 增加（均 P ≤ 0.001）。

结论

TMS 线圈方向和肌肉激活影响在胫骨前部记录的皮质内兴奋性的测量，因此是下肢肌肉 TMS 研究的重要考虑因素。