Toronto Western Hospital, 399 Bathurst Street, Toronto, Ontario M5T 2S8, Canada.
J Physiol. 2009 Dec 1;587(Pt 23):5665-78. doi: 10.1113/jphysiol.2009.181446. Epub 2009 Oct 12.
Short interval intracortical facilitation (SICF) can be elicited by transcranial magnetic stimulation (TMS) of the motor cortex (M1) with a suprathreshold first stimulus (S1) followed by a subthreshold second stimulus (S2). SICF occurs at three distinct phases and is likely to be related to the generation of indirect (I) waves. Short interval intracortical inhibition (SICI) is an inhibitory phenomenon and intracortical facilitation (ICF) is an excitatory phenomenon occurring in the M1 that can be studied with TMS. We studied the interactions between SICI/ICF and SICF in 17 healthy subjects. Six experiments were conducted. The first experiment examined the effects of different S1 intensities on SICI, ICF and SICF at three peaks. The effects of SICI on SICF were tested by a triple-pulse TMS protocol in the second experiment. We performed Experiments 3-5 to further test the interactions between SICI and SICF with various strengths of SICI, at SICF peaks and troughs, and with SICF generated by different current direction which preferentially generates late I waves. The effects of ICF on SICF were examined in Experiment 6. The results showed that ICF and SICF decreased whereas SICI increased with higher S1 intensities. SICI facilitated SICF mediated by late I waves both at the peaks and the troughs of SICF. The increase of SICF in the presence of SICI correlated to the strength of SICI. ICF decreased the third peak of SICF. We conclude that SICI facilitates SICF at neuronal circuits responsible for generating late I waves through disinhibition, while ICF may have the opposite effects.
短间隔皮质内易化（SICF）可通过经颅磁刺激（TMS）于运动皮质（M1）诱发，采用阈上的第一刺激（S1）后跟随阈下的第二刺激（S2）。SICF 出现于三个不同的时相，可能与间接（I）波的产生相关。短间隔皮质内抑制（SICI）为抑制现象，皮质内易化（ICF）为兴奋性现象，可通过 TMS 进行研究。我们于 17 名健康受试者中研究 SICI/ICF 与 SICF 之间的相互作用。进行了六项实验。第一项实验考察了不同 S1 强度对三个峰值的 SICI、ICF 和 SICF 的影响。第二项实验采用三脉冲 TMS 方案测试了 SICI 对 SICF 的影响。我们进行了实验 3-5，进一步以不同的 SICI 强度、在 SICF 的波峰和波谷、以及利用更易产生晚期 I 波的不同电流方向产生的 SICF，测试 SICI 与 SICF 之间的相互作用。实验 6 考察了 ICF 对 SICF 的影响。结果显示，随着 S1 强度的增加，ICF 和 SICF 降低，而 SICI 增加。SICI 通过晚期 I 波易化了 SICF，这一作用存在于 SICF 的波峰和波谷处。SICI 存在时 SICF 的增加与 SICI 的强度相关。ICF 降低了 SICF 的第三个峰值。我们的结论是，SICI 通过去抑制作用易化了产生晚期 I 波的神经元回路中的 SICF，而 ICF 可能具有相反的作用。
