Two phases of short-interval intracortical inhibition
Two phases of short-interval intracortical inhibition
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DOI：
10.1007/s00221-003-1502-9
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发表时间：
2003-08-01
影响因子：
2
通讯作者：
Chen, R
中科院分区：
文献类型：
--
作者：
Roshan, L;Paradiso, GO;Chen, R
短间隔皮质内抑制（SICI）是一种广泛使用的研究皮质抑制的方法，在一些神经和精神疾病中发现了异常。以往的研究表明SICI包括两个阶段，第一个阶段可以用轴突耐火性来解释。我们的目标是进一步研究SICI的两个阶段的机制。在11名正常志愿者中，采用配对经颅磁刺激（TMS）模式对左运动皮层进行SICI研究，该模式采用阈下条件刺激（休息状态下80%的静息运动阈值和活动状态下95%的活动运动阈值），然后以1-4.5 ms的刺激间隔（ISIs）为间隔，以0.5 ms的步骤进行阈上测试刺激。记录右第一背骨间肌运动诱发电位（MEPs）。在目标肌肉放松和20%最大收缩时，研究了三种不同的测试刺激强度，分别在休息时产生0.2、1和4 mV的mep。在静息状态下，ISIs为1 ms和2.5 ms时，抑制作用最大，ISIs之间的差异随着自愿收缩而减小。SICI随MEP振幅增大而增大，随自发性收缩而减小。在0.2 mV的MEP下，部分受试者表现出易化，这可能与短间隔皮层内易化有关。对于休息SICI，相邻ISIs之间的相关性在3 - 4.5 ms之间远高于1 - 2.5 ms或1 - 2.5 ms之间。不同测试MEP振幅下的SICI无相关性。我们得出结论，在1和2.5 ms的ISIs下，最大SICI是由不同的机制介导的。1 ms时的SICI不能完全用轴突难解性来解释，可能涉及突触抑制。SICI是一个复杂的现象，不同ISIs的抑制可能由不同的抑制回路介导。
Short-interval intracortical inhibition (SICI) is a widely used method to study cortical inhibition, and abnormalities have been found in several neurological and psychiatric disorders. Previous studies suggested that SICI involves two phases and the first phase may be explained by axonal refractoriness. Our objectives are to further investigate the mechanisms of the two phases of SICI. SICI was studied in 11 normal volunteers by a paired transcranial magnetic stimulation (TMS) paradigm applied to the left motor cortex with a subthreshold conditioning stimulus (80% resting motor threshold for rest condition and 95% active motor threshold for active condition) followed by a suprathreshold test stimulus at interstimulus intervals (ISIs) of 1-4.5 ms in steps of 0.5 ms. Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous muscle. Three different test stimulus intensities adjusted to produce 0.2, 1 and 4 mV MEPs at rest were studied with the target muscle relaxed and during 20% maximum contraction. Maximum inhibition was observed at ISIs of 1 ms and 2.5 ms for the rest condition and the difference among ISIs was reduced with voluntary contraction. SICI increased with larger test MEP amplitude and decreased with voluntary contraction. At test MEP of 0.2 mV, some subjects showed facilitation and this is likely related to short-interval intracortical facilitation. For rest SICI, the correlation between adjacent ISIs was much higher from 3 to 4.5 ms than from 1 to 2.5 ms or between 1 and 2.5 ms. There was no correlation between SICI at different test MEP amplitudes. We conclude that maximum SICI at ISIs of 1 and 2.5 ms are mediated by different mechanisms. SICI at 1 ms cannot be fully explained by axonal refractoriness and synaptic inhibition may be involved. SICI is a complex phenomenon and inhibition at different ISIs may be mediated by different inhibitory circuits.