Department of Clinical Neurophysiology, University Medical Center Göttingen, Robert-Koch-Str 40, 37075 Göttingen, Germany.
Brain Stimul. 2013 May;6(3):363-70. doi: 10.1016/j.brs.2012.07.003. Epub 2012 Aug 1.
Directional sensitivity is relevant for the excitability threshold of the human primary motor cortex, but its importance for externally induced plasticity is unknown.
To study the influence of current direction on two paradigms inducing neuroplasticity by repetitive transcranial magnetic stimulation (rTMS).
We studied short-lasting after-effects induced in the human primary motor cortex of 8 healthy subjects, using 5 Hz rTMS applied in six blocks of 200 pulses each, at 90% active motor threshold. We controlled for intensity, frequency, waveform and spinal effects.
Only biphasic pulses with the effective component delivered in an anterioposterior direction (henceforth posteriorly directed) in the brain yielded an increase of motor-evoked potential (MEP) amplitudes outlasting rTMS. MEP latencies and F-wave amplitudes remained unchanged. Biphasic pulses directed posteroanterior (i.e. anteriorly) were ineffective, as were monophasic pulses from either direction. A 1 Hz study in a group of 12 healthy subjects confirmed facilitation after posteriorly directed biphasic pulses only.
The anisotropy of the human primary motor cortex is relevant for induction of plasticity by subtreshold rTMS, with a current flow opposite to that providing lowest excitability thresholds. This is consistent with the idea of TMS primarily targeting cortical columns of the phylogenetically new M1 in the anterior bank of the central sulcus. For these, anteriorly directed currents are soma-depolarizing, therefore optimal for low thresholds, whereas posteriorly directed currents are soma-hyperpolarizing, likely dendrite-depolarizing and bested suited for induction of plasticity. Our findings should help focus and enhance rTMS effects in experimental and clinical settings.
方向性敏感性与人类初级运动皮层的兴奋性阈值有关，但它对外部诱导的可塑性的重要性尚不清楚。
研究电流方向对两种通过重复经颅磁刺激（rTMS）诱导神经可塑性的范式的影响。
我们研究了 8 名健康受试者的初级运动皮层中短暂的后效，使用 5 Hz rTMS 在 90%的主动运动阈值下施加 6 个 200 脉冲的块，每个块 200 脉冲。我们控制了强度、频率、波形和脊髓效应。
只有在大脑中以前后方向（后文称为向后）传递有效成分的双相脉冲才能产生持续时间长于 rTMS 的运动诱发电位（MEP）幅度增加。MEP 潜伏期和 F 波幅度保持不变。向后（即向前）的双相脉冲以及来自任何方向的单相脉冲都没有效果。一组 12 名健康受试者的 1 Hz 研究证实，仅向后双相脉冲可产生易化作用。
人类初级运动皮层的各向异性与亚阈值 rTMS 诱导可塑性有关，电流方向与提供最低兴奋性阈值的方向相反。这与 TMS 主要靶向中央沟前壁新进化的 M1 的皮质柱的观点一致。对于这些皮质柱，向前的电流使胞体去极化，因此最适合低阈值，而向后的电流使胞体超极化，可能使树突去极化，最适合诱导可塑性。我们的发现应该有助于在实验和临床环境中集中和增强 rTMS 的效果。
