Intracortical circuits modulate transcallosal inhibition in humans
Intracortical circuits modulate transcallosal inhibition in humans
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DOI：
10.1113/jphysiol.2007.134510
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发表时间：
2007-08-15
影响因子：
5.5
通讯作者：
Rothwell, J. C.
中科院分区：
文献类型：
--
作者：
Avanzino, L.;Teo, J. T. H.;Rothwell, J. C.
先前的研究结果使用成对脉冲经颅磁刺激（TMS）表明，兴奋性的transcallosa（TC）的两个运动皮层的手区域之间的连接是由皮质内抑制回路调制的方式相同的皮质脊髓束（CTS）的预测脊髓运动神经元。在这里，我们描述了TC和CTS控制中的两个进一步的相似之处：（1）I波易化方案和（2）rTMS预处理。在实验1中，TC通路的兴奋性测量使用半球间抑制（IHI）和同侧沉默期（iSP），而CTS通路的兴奋性测量记录的EMG反应诱发的第一背侧骨间肌对侧的条件刺激（cMEP）。首先将条件刺激的强度调整到诱发IHI和iSP的阈值，然后以1.3至4.3 ms的刺激间隔（ISI）随机施加成对的条件刺激。IHI和iSP分别在ISI = 1.5 ms和3.0 ins时被促进，对侧手的条件刺激诱发MEP也是如此。我们认为，TC预测收到类似于CTS预测中看到的I波的促进。在实验2中，在90%静息运动阈值下，在600个5 Hz rTMS脉冲之前和之后检测iSP的短间隔抑制（SICIisp）和cMEP的短间隔皮质内抑制（SICIcMEP）。SICIiSP和SICIcMEP均降低，iSP也是如此; cMEP无变化。这表明，控制TC神经元的抑制性中间神经元群体以与控制CTS神经元的抑制性中间神经元群体相同的方式对5 Hz rTMS作出响应。两者合计，从两个实验的数据表明，第III层和第V层锥体神经元，分别引起TC和CTS途径，是由具有相似特性的神经元回路控制。
Previous results using paired-pulse transcranial magnetic stimulation (TMS) have suggested that the excitability of transcallosal (TC) connections between the hand areas of the two motor cortices is modulated by intracortical inhibitory circuits in the same way as corticospinal tract (CTS) projections to spinal motoneurons. Here we describe two further similarities in TC and CTS control using (1) an I-wave facilitation protocol and (2) preconditioning with rTMS. In experiment 1, excitability of TC pathways was measured using interhemispheric inhibition (IHI) and the ipsilateral silent period (iSP), whilst excitability of CTS pathways was measured by recording the EMG response evoked in the first dorsal interosseous muscle contralateral to the conditioning stimulus (cMEP). The intensity of the conditioning stimulus was first adjusted to threshold for evoking IHI and iSP, then pairs of conditioning stimuli were applied randomly at interstimulus intervals (ISIs) from 1.3 to 4.3 ms. IHI and iSP were facilitated at ISI = 1.5 ms and 3.0 ins, respectively, as was the MEP evoked by the conditioning stimuli in the contralateral hand. We suggest that TC projections receive I-wave-like facilitation similar to that seen in CTS projections. In experiment 2, short interval inhibition of the iSP (SICIisp), and short interval intracortical inhibition of the cMEP (SICIcMEP) were examined before and after 600 pulses of 5 Hz rTMS at 90% resting motor threshold. Both SICIiSP and SICIcMEP were reduced, as was the iSP; the cMEP was unchanged. This shows that the population of inhibitory interneurons that control TC neurons respond in the same way to 5 Hz rTMS as those that control CTS neurons. Taken together, the data from the two experiments suggest that the layer III and layer V pyramidal neurons that give rise to TC and CTS pathways, respectively, are controlled by neuronal circuitry with similar properties.