Delvendahl Igor, Gattinger Norbert, Berger Thomas, Gleich Bernhard, Siebner Hartwig R, Mall Volker
Carl-Ludwig-Institute for Physiology, Leipzig University, Leipzig, Germany.
Zentralinstitut für Medizintechnik, Technische Universität München (IMETUM), Garching, Germany.
PLoS One. 2014 Dec 16;9(12):e115247. doi: 10.1371/journal.pone.0115247. eCollection 2014.
A full-sine (biphasic) pulse waveform is most commonly used for repetitive transcranial magnetic stimulation (TMS), but little is known about how variations in duration or amplitude of distinct pulse segments influence the effectiveness of a single TMS pulse to elicit a corticomotor response. Using a novel TMS device, we systematically varied the configuration of full-sine pulses to assess the impact of configuration changes on resting motor threshold (RMT) as measure of stimulation effectiveness with single-pulse TMS of the non-dominant motor hand area (M1). In young healthy volunteers, we (i) compared monophasic, half-sine, and full-sine pulses, (ii) applied two-segment pulses consisting of two identical half-sines, and (iii) manipulated amplitude, duration, and current direction of the first or second full-sine pulse half-segments. RMT was significantly higher using half-sine or monophasic pulses compared with full-sine. Pulses combining two half-sines of identical polarity and duration were also characterized by higher RMT than full-sine stimuli resulting. For full-sine stimuli, decreasing the amplitude of the half-segment inducing posterior-anterior oriented current in M1 resulted in considerably higher RMT, whereas varying the amplitude of the half-segment inducing anterior-posterior current had a smaller effect. These findings provide direct experimental evidence that the pulse segment inducing a posterior-anterior directed current in M1 contributes most to corticospinal pathway excitation. Preferential excitation of neuronal target cells in the posterior-anterior segment or targeting of different neuronal structures by the two half-segments can explain this result. Thus, our findings help understanding the mechanisms of neural stimulation by full-sine TMS.
全正弦（双相）脉冲波形最常用于重复经颅磁刺激（TMS），但对于不同脉冲段的持续时间或幅度变化如何影响单个TMS脉冲引发皮质运动反应的有效性，人们了解甚少。我们使用一种新型TMS设备，系统地改变全正弦脉冲的配置，以评估配置变化对静息运动阈值（RMT）的影响，以此作为非优势运动手区（M1）单脉冲TMS刺激有效性的指标。在年轻健康志愿者中，我们（i）比较了单相、半正弦和全正弦脉冲，（ii）应用了由两个相同半正弦组成的两段式脉冲，以及（iii）操纵了第一个或第二个全正弦脉冲半段的幅度、持续时间和电流方向。与全正弦脉冲相比，使用半正弦或单相脉冲时RMT显著更高。组合两个极性和持续时间相同的半正弦的脉冲，其RMT也高于全正弦刺激。对于全正弦刺激，降低在M1中诱导后向前定向电流的半段的幅度会导致RMT大幅升高，而改变诱导前向后电流的半段的幅度影响较小。这些发现提供了直接的实验证据，表明在M1中诱导后向前定向电流的脉冲段对皮质脊髓通路的兴奋贡献最大。后向前段中神经元靶细胞的优先兴奋或两个半段对不同神经元结构的靶向作用可以解释这一结果。因此，我们的发现有助于理解全正弦TMS的神经刺激机制。
