Vassiliadis Pierre, Grandjean Julien, Derosiere Gerard, de Wilde Ysaline, Quemener Louise, Duque Julie
Institute of Neuroscience, Université Catholique de Louvain, Brussels, Belgium.
Front Neurosci. 2018 Mar 8;12:139. doi: 10.3389/fnins.2018.00139. eCollection 2018.
Transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1), elicits motor-evoked potentials (MEPs) in contralateral limb muscles which are valuable indicators of corticospinal excitability (CSE) at the time of stimulation. So far, most studies have used single-coil TMS over one M1, yielding MEPs in muscles of a single limb-usually the hand. However, tracking CSE in the two hands simultaneously would be useful in many contexts. We recently showed that, in the resting state, double-coil stimulation of the two M1 with a 1 ms inter-pulse interval (double-coil TMS) elicits MEPs in both hands that are comparable to MEPs obtained using single-coil TMS. To further evaluate this new technique, we considered the MEPs elicited by double-coil TMS in an instructed-delay choice reaction time task where a prepared response has to be withheld until an imperative signal is displayed. Single-coil TMS studies have repetitively shown that in this type of task, the motor system is transiently inhibited during the delay period, as evident from the broad suppression of MEP amplitudes. Here, we aimed at investigating whether a comparable inhibitory effect can be observed with MEPs elicited using double-coil TMS. To do so, we compared the amplitude as well as the coefficient of variation (CV) of MEPs produced by double-coil or single-coil TMS during action preparation. We observed that MEPs were suppressed (smaller amplitude) and often less variable (smaller CV) during the delay period compared to baseline. Importantly, these effects were equivalent whether single-coil or double-coil TMS was used. This suggests that double-coil TMS is a reliable tool to assess CSE, not only when subjects are at rest, but also when they are involved in a task, opening new research horizons for scientists interested in the corticospinal correlates of human behavior.
经颅磁刺激（TMS）作用于初级运动皮层（M1）时，会在对侧肢体肌肉中诱发运动诱发电位（MEP），这些电位是刺激时皮质脊髓兴奋性（CSE）的重要指标。到目前为止，大多数研究都在一个M1上使用单线圈TMS，在单肢体（通常是手部）的肌肉中产生MEP。然而，在许多情况下，同时追踪两只手的CSE会很有用。我们最近发现，在静息状态下，以1毫秒的脉冲间隔对两个M1进行双线圈刺激（双线圈TMS），会在两只手中诱发与使用单线圈TMS获得的MEP相当的MEP。为了进一步评估这项新技术，我们考虑了在指令延迟选择反应时间任务中双线圈TMS诱发的MEP，在该任务中，准备好的反应必须被抑制，直到显示出命令信号。单线圈TMS研究反复表明，在这种类型的任务中，运动系统在延迟期会被短暂抑制，MEP幅度的广泛抑制就证明了这一点。在这里，我们旨在研究使用双线圈TMS诱发的MEP是否能观察到类似的抑制作用。为此，我们比较了双线圈或单线圈TMS在动作准备期间产生的MEP的幅度以及变异系数（CV）。我们观察到，与基线相比，延迟期的MEP被抑制（幅度较小），且通常变异性较小（CV较小）。重要的是，无论使用单线圈还是双线圈TMS，这些效应都是相同的。这表明双线圈TMS不仅是评估受试者静息时CSE的可靠工具，也是评估他们参与任务时CSE的可靠工具，为对人类行为的皮质脊髓相关性感兴趣的科学家开辟了新的研究视野。
