Aix-Marseille Université, CNRS, UMR 7291, 13331 Marseille cedex, France.
Neuroscience. 2013 Aug 29;246:329-41. doi: 10.1016/j.neuroscience.2013.05.005. Epub 2013 May 11.
When our movement is perturbed by environmental forces, the Long Latency Stretch Reflex (LLSR), generated by a transcortical loop through the primary motor cortex (M1), is the fastest reaction adapted according to our prior intent. We investigated the involvement of the caudal part of the Supplementary Motor Area (SMAp) in this intention-related LLSR modulation. Subjects were instructed either to not react (i.e. to 'let-go') or to resist a mechanical perturbation extending the wrist and Transcranial Magnetic Stimulation (TMS) was used to transiently inactivate SMAp, either at the time of the LLSR generation (TMS was applied 50 ms before the perturbation), or at the end of the preparation period (TMS was applied 150 ms before the perturbation). The effect of SMAp transient inactivation on the LLSR modulation was compared to the effect of transient inactivation of M1 or of a Control area. Compared to the Control condition, the intention-related LLSR modulation decreased when TMS was applied either over SMAp or over M1 50 ms before perturbation occurrence, suggesting that SMAp, as M1, is involved in the LLSR modulation. Moreover, the LLSR modulation also decreased when TMS was applied over SMAp 150 ms before the perturbation, indicating that anticipatory processes taking place in SMAp participate to the LLSR modulation. In addition, TMS applied over SMAp elicited Motor-Evoked Potentials (MEPs) whose latency and shape were similar to MEPs evoked by TMS over M1, suggesting that they are due to direct corticospinal projections from SMAp. Interestingly, the SMAp MEPs amplitude was modulated depending on the subject's intention to resist or to let-go. Taken together these results strongly favor the idea that, during the expectation of a perturbation, SMAp is the seat of anticipatory processes that are specific to the subject's intent and that preset M1 in order to adapt the LLSR to this intention.
当我们的运动受到环境力的干扰时，通过初级运动皮层 (M1) 的皮质下环路产生的长潜伏期伸展反射 (LLSR) 是根据我们先前的意图做出的最快反应适应。我们研究了补充运动区 (SMAp) 的尾部部分在这种与意图相关的 LLSR 调制中的参与。受试者被指示要么不反应（即“放手”），要么抵抗机械干扰，伸展手腕，同时使用经颅磁刺激 (TMS) 暂时失活 SMAp，要么在 LLSR 产生时（TMS 在干扰发生前 50 毫秒施加），要么在准备期结束时（TMS 在干扰发生前 150 毫秒施加）。与瞬时光滑失活 M1 或对照区相比，SMAp 瞬时光滑失活对 LLSR 调制的影响与 SMAp 或 M1 上的 TMS 应用在干扰发生前 50 毫秒相比，意图相关的 LLSR 调制减弱，表明 SMAp 与 M1 一样，参与了 LLSR 调制。此外，当 TMS 在干扰发生前 150 毫秒施加于 SMAp 时，LLSR 调制也减弱，表明在 SMAp 中发生的预期过程参与了 LLSR 调制。此外，施加于 SMAp 的 TMS 诱发电动诱发电位 (MEPs) 的潜伏期和形状与施加于 M1 的 TMS 诱发电动诱发电位相似，表明它们是由于 SMAp 的直接皮质脊髓投射。有趣的是，SMAp 的 MEPs 幅度取决于受试者抵抗或放手的意图。总之，这些结果强烈支持这样一种观点，即在预期干扰时，SMAp 是预期过程的所在地，这些过程是特定于受试者的意图，并预先设定 M1，以便使 LLSR 适应这种意图。
