Discipline of Physiology, University of Adelaide, Adelaide, Australia.
Eur J Neurosci. 2023 Sep;58(5):3270-3285. doi: 10.1111/ejn.16099. Epub 2023 Jul 27.
Repetitive paired-pulse transcranial magnetic stimulation (TMS) at indirect (I)-wave periodicity (iTMS) can increase plasticity in primary motor cortex (M1). Both TMS coil orientation and muscle activation can influence I-wave activity, but it remains unclear how these factors influence M1 plasticity with iTMS. We therefore investigated the influence of TMS coil orientation and muscle activation on the response to iTMS. Thirty-two young adults (24.2 ± 4.8 years) participated in three experiments. Each experiment included two sessions using a modified iTMS intervention with either a posterior-anterior orientation (PA) or anterior-posterior (AP) coil orientation over M1. Stimulation was applied in resting (Experiments 1 and 3) or active muscle (Experiments 2 and 3). Effects of iTMS on M1 excitability were assessed by recording motor evoked potentials (MEPs) and short-interval intracortical facilitation (SICF) with PA and AP orientations in both resting (all experiments) and active (Experiment 2) muscle. For the resting intervention, MEPs were greater after AP iTMS (Experiment 1, P = .046), whereas SICF was comparable between interventions (all P > .10). For the active intervention, responses did not vary between PA and AP iTMS (Experiment 2, all P > .14), and muscle activation reduced the effect of AP iTMS during the intervention (Experiment 3, P = .002). Coil orientation influenced the MEP response after iTMS, and muscle activation reduced the response during iTMS. While this suggests that AP iTMS may be beneficial in producing a neuroplastic modulation of I-wave circuits in resting muscle, further exploration of factors such as dosing is required.
重复经颅磁刺激（TMS）的间接（I）波周期性（iTMS）可增加初级运动皮层（M1）的可塑性。TMS 线圈方向和肌肉激活都可以影响 I 波活动，但尚不清楚这些因素如何影响 iTMS 对 M1 可塑性的影响。因此，我们研究了 TMS 线圈方向和肌肉激活对 iTMS 反应的影响。32 名年轻成年人（24.2±4.8 岁）参加了三项实验。每个实验都包括两个使用改良 iTMS 干预的会话，其中 M1 上的 TMS 线圈方向为前后（PA）或前后（AP）。刺激在休息（实验 1 和 3）或主动肌肉（实验 2 和 3）中施加。通过在休息（所有实验）和主动（实验 2）肌肉中记录运动诱发电位（MEPs）和短间隔内皮层易化（SICF），评估 iTMS 对 M1 兴奋性的影响。使用 PA 和 AP 方向。对于休息干预，AP iTMS 后 MEP 更大（实验 1，P=.046），而干预之间的 SICF 相似（所有 P>.10）。对于主动干预，PA 和 AP iTMS 之间的反应没有差异（实验 2，所有 P>.14），并且肌肉激活减少了干预期间 AP iTMS 的反应（实验 3，P=.002）。线圈方向影响 iTMS 后的 MEP 反应，而肌肉激活则降低了 iTMS 期间的反应。虽然这表明 AP iTMS 可能有益于在休息肌肉中产生 I 波电路的神经可塑性调节，但需要进一步探索剂量等因素。
