Intensity-Dependent Effects of Low-Frequency Subthreshold rTMS on Primary Motor Cortex Excitability and Interhemispheric Inhibition in Elderly Participants: A Randomized Trial.

Neurorehabilitation and neural repair Pub Date : 2025-01-01 Epub Date: 2024-10-27 DOI:10.1177/15459683241292615

Miles Wischnewski, Lauren Edwards, Kate P Revill, Daniel Drake, Gerald Hobbs, Cathrin M Buetefisch

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Abstract

Background: Low-frequency repetitive transcranial magnetic stimulation (LF-rTMS) protocols targeting primary motor cortex (M1) are used in rehabilitation of neurological diseases for their therapeutic potential, safety, and tolerability. Although lower intensity LF-rTMS can modulate M1 neurophysiology, results are variable, and a systematic assessment of its dose effect is lacking.

Objectives: To determine the dose-response of LF-rTMS on stimulated and non-stimulated M1.

Methods: In a sham-controlled randomized double-blind crossover study the effect of LF-TMS protocols were determined in 20 right-handed older healthy participants. In 3 sessions, 1 Hz rTMS at 80% (rTMS₈₀), 90% (rTMS₉₀) of motor threshold or sham stimulation were applied to left upper extremity M1. Outcome measures were curve parameters of the stimulus-response curve (maximum motor evoked potential [MEP_MAX], slope and the intensity to evoke 50% MEP_MAX), short-interval intracortical inhibition (SICI), and interhemispheric inhibition (IHI).

Results: Within LF-rTMS sessions, rTMS₉₀, increased MEP_MAX in the stimulated M1. Furthermore, rTMS₉₀, increased the slope in the non-stimulated M1. LF-rTMS effects on SICI were dependent on the participants' baseline SICI, hemisphere, and intensity of conditioning pulse. Finally, rTMS₉₀ increased whereas rTMS₈₀ decreased IHI, for both IHI directions. These changes were dependent on baseline IHI and hemisphere and were no longer significant when baseline IHI was accounted for.

Conclusions: Intensity of subthreshold LF-rTMS has differential effects on excitation and inhibition of stimulated and non-stimulated M1. The effects were small and were only demonstrated within the LF-rTMS sessions but were not different when compared to sham. rTMS related changes in SICI and IHI were dependent on baseline level.

Clinicaltrials.gov identifier: NCT02544503, NCT01726218.

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低频阈下经颅磁刺激对老年人初级运动皮层兴奋性和半球间抑制的强度依赖效应：随机试验

背景：针对初级运动皮层（M1）的低频重复经颅磁刺激（LF-rTMS）方案因其治疗潜力、安全性和耐受性而被用于神经系统疾病的康复治疗。虽然较低强度的低频经颅磁刺激可以调节 M1 神经生理学，但结果不一，而且缺乏对其剂量效应的系统评估：确定低频经颅磁刺激对受刺激和非受刺激 M1 的剂量反应：在一项假对照随机双盲交叉研究中，确定了 20 名右手健康的老年参与者的低频经颅磁刺激方案的效果。在 3 个疗程中，分别对左上肢 M1 进行运动阈值 80% (rTMS80)、90% (rTMS90) 的 1 Hz 经颅磁刺激或假刺激。结果测量指标为刺激-反应曲线参数（最大运动诱发电位[MEPMAX]、斜率和唤起50% MEPMAX的强度）、短间隔皮层内抑制（SICI）和半球间抑制（IHI）：结果：在低频经颅磁刺激疗程中，经颅磁刺激 90 增加了受刺激 M1 的 MEPMAX。此外，经颅磁刺激 90 还增加了非刺激 M1 的斜率。低频经颅磁刺激对 SICI 的影响取决于参与者的基线 SICI、半球和调节脉冲强度。最后，在两个 IHI 方向上，rTMS90 增加了 IHI，而 rTMS80 减少了 IHI。这些变化取决于基线 IHI 和半球，当基线 IHI 考虑在内时，这些变化不再显著：结论：阈下低频经颅磁刺激的强度对受刺激和非受刺激 M1 的兴奋和抑制有不同的影响。经颅磁刺激相关的 SICI 和 IHI 变化取决于基线水平：NCT02544503、NCT01726218。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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Neurorehabilitation and neural repair

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