Organization of ipsilateral excitatory and inhibitory pathways in the human motor cortex
Organization of ipsilateral excitatory and inhibitory pathways in the human motor cortex
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DOI：
10.1152/jn.00950.2002
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发表时间：
2003-03-01
影响因子：
2.5
通讯作者：
Li, JY
中科院分区：
文献类型：
--
作者：
Chen, R;Yung, D;Li, JY
运动皮质刺激对同侧肌肉有兴奋和抑制作用。兴奋效应可以通过同侧运动诱发电位（iMEPs）来评估。抑制作用包括被称为沉默期（iSP）的同侧随意肌活动的中断，以及对侧运动皮层条件刺激引起的皮质脊髓兴奋性的降低（半球间抑制，IHI）。iSP和IHI都可能通过经胼胝体通路介导。它们与对侧皮质脊髓投射的关系以及iSP和IHI是否代表相同的现象仍然是核心的。经颅磁刺激（TMS）激活的神经元群高度依赖于脑内感应电流的方向。通过观察不同刺激强度和电流方向的影响，我们研究了iMEP、iSP、IHI和对侧皮质脊髓系统之间的关系。记录双侧第一背骨间肌的肌表电图（EMG）。右侧FDI肌的iSP是在随意肌收缩时通过右侧运动皮层刺激获得的。在刺激间隔（ISIs） 2- 80ms时，通过对右侧运动皮层进行条件刺激，然后对左侧运动皮层进行测试刺激来检测IHI。右侧运动皮层感应电流方向为前内侧（AM）、后内侧（PM）、后外侧和前外侧（AL）。对侧MEPs （cMEPs）在AM方向的阈值最低，在PM方向的潜伏期最短。10名受试者中有8名存在iMEPs。iMEP和IHI均未表现出明显的定向偏好。所有被试均表现为AL方向阈值最高，AM方向持续时间最长。cMEP、iSP和IHI都随着刺激强度的增加而增加，达到刺激器输出的75%左右。靶肌激活降低了8 ms ISI时的IHI，但对40 ms ISI时的IHI影响不大。在任何刺激强度和电流方向下，8 ms ISI的iSP和IHI都不相关，因子分析表明它们是由不同的因素解释的。然而，40毫秒ISI时的活跃IHI可以用与iSP相同的因素来解释。与iMEP和IHI相比，cMEP的不同方向偏好表明，这些同侧效应是由不同于激活皮质脊髓神经元的皮质神经元群体介导的。iSP和IHI不代表相同的现象，应被视为同侧抑制的补充措施。
Motor cortex stimulation has both excitatory and inhibitory effects on ipsilateral muscles. Excitatory effects can be assessed by ipsilateral motor-evoked potentials (iMEPs). Inhibitory effects include an interruption of ipsilateral voluntary muscle activity known as the silent period (iSP) and a reduction in corticospinal excitability evoked by conditioning stimulation of the contralateral motor cortex (interhemispheric inhibition, IHI). Both iSP and IHI may be mediated by transcallosal pathways. Their relationship to the contralateral corticospinal projection and whether iSP and IHI represent the same phenomenon remain nuclear. The neuronal population activated by transcranial magnetic stimulation (TMS) is highly dependent on the direction of the induced current in the brain. We examined the relationship among iMEP, iSP, IHI, and the contralateral corticospinal system by examining the effects of different stimulus intensities and current directions. Surface electromyography (EMG) was recorded from both first dorsal interosseous (FDI) muscles. The iSP in the right FDI muscle was obtained by right motor cortex stimulation during voluntary muscle contraction. IHI was examined by conditioning stimulation of the right motor cortex followed by test stimulation of the left motor cortex at interstimulus intervals (ISIs) of 2-80 ms. The induced current directions tested in the right motor cortex were anterior medial (AM), posterior medial (PM), posterior lateral, and anterior lateral (AL). Contralateral MEPs (cMEPs) had the lowest threshold with the AM direction and the shortest latency with the PM direction. iMEPs were present in 8 of 10 subjects. Both iMEP and IHI did not show significant directional preference. iSP was observed in all subjects with the highest threshold for the AL direction and the longest duration for the AM direction. cMEP, iSP, and IHI all increased with stimulus intensity up to similar to75% stimulator output. Target muscle activation decreased IHI at 8-ms ISI but had little effect on IHI at 40-ms ISI. iSP and IHI at 8-ms ISI did not correlate at any stimulus intensities and current directions tested, and factor analysis showed that they are explained by different factors. However, active IHI at 40-ms ISI was explained by the same factor as iSP. The different directional preference for cMEP compared with iMEP and IHI suggests that these ipsilateral effects are mediated by populations of cortical neurons that are different from those activating the corticospinal neurons. iSP and IHI do not represent the same phenomenon and should be considered complementary measures of ipsilateral inhibition.