Selective Suppression of Local Interneuron Circuits in Human Motor Cortex Contributes to Movement Preparation.
Selective Suppression of Local Interneuron Circuits in Human Motor Cortex Contributes to Movement Preparation.
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DOI：
10.1523/jneurosci.2869-17.2017
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发表时间：
2018-01-31
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影响因子：
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通讯作者：
Rothwell JC
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作者：
Hannah R;Cavanagh SE;Tremblay S;Simeoni S;Rothwell JC
运动前运动皮层的神经活动会发生变化，但这种准备活动的性质和目的尚不清楚。为了无创地研究人类（包括男性和女性）大脑中的这一现象，我们在各种反应时任务的预警期内，使用经颅磁刺激（TMS）来探测皮质脊髓神经元不同组兴奋性输入的兴奋性。通过两种独立的方法（H反射调节和TMS的方向效应），我们发现皮质脊髓神经元的一组特定兴奋性输入在运动准备过程中受到抑制，而另一组输入则不受影响。为了探究这种抑制的行为相关性，我们检查了每次试验中选择性准备性抑制的强度是否与反应时相关。令人惊讶的是，选择性准备性抑制的程度越大，反应时越快。这表明对皮质脊髓神经元输入的抑制并非用于阻止运动的释放，实际上可能促进快速反应。因此，对一组特定运动皮层神经元的选择性抑制可能是成功的运动准备的一个关键方面。
《意义声明》尽管没有明显的运动，但运动准备会在运动皮层引发大量活动。对于没有运动这一现象的一种解释是，在此期间运动皮层的输出受到一种抑制机制的控制。先前对人类运动皮层的无创TMS研究表明皮质脊髓兴奋性降低，这支持了上述观点。相反，我们的数据支持这样一种观点，即皮质脊髓输出神经元上游的活动存在一种协调的平衡。这包括对特定局部回路的抑制，这种抑制支持而非抑制已准备好的运动的快速产生。因此，对局部回路的选择性抑制似乎是成功的运动准备的一个重要部分，而非一种外部控制机制。
Changes in neural activity occur in the motor cortex before movement, but the nature and purpose of this preparatory activity is unclear. To investigate this in the human (male and female) brain noninvasively, we used transcranial magnetic stimulation (TMS) to probe the excitability of distinct sets of excitatory inputs to corticospinal neurons during the warning period of various reaction time tasks. Using two separate methods (H-reflex conditioning and directional effects of TMS), we show that a specific set of excitatory inputs to corticospinal neurons are suppressed during motor preparation, while another set of inputs remain unaffected. To probe the behavioral relevance of this suppression, we examined whether the strength of the selective preparatory inhibition in each trial was related to reaction time. Surprisingly, the greater the amount of selective preparatory inhibition, the faster the reaction time was. This suggests that the inhibition of inputs to corticospinal neurons is not involved in preventing the release of movement but may in fact facilitate rapid reactions. Thus, selective suppression of a specific set of motor cortical neurons may be a key aspect of successful movement preparation. SIGNIFICANCE STATEMENT Movement preparation evokes substantial activity in the motor cortex despite no apparent movement. One explanation for the lack of movement is that motor cortical output in this period is gated by an inhibitory mechanism. This notion was supported by previous noninvasive TMS studies of human motor cortex indicating a reduction of corticospinal excitability. On the contrary, our data support the idea that there is a coordinated balance of activity upstream of the corticospinal output neurons. This includes a suppression of specific local circuits that supports, rather than inhibits, the rapid generation of prepared movements. Thus, the selective suppression of local circuits appears to be an essential part of successful movement preparation instead of an external control mechanism.