Shirley Ryan AbilityLab, Chicago, Illinois, United States.
Department of Physical Therapy and Human Movement Sciences, Northwestern University, Chicago, Illinois, United States.
J Neurophysiol. 2023 Sep 1;130(3):788-797. doi: 10.1152/jn.00207.2023. Epub 2023 Jul 12.
Electrophysiological studies in nonhuman primates reported the existence of strong corticospinal output from the primary motor cortex to distal compared with proximal hindlimb muscles. The extent to which corticospinal output differs across muscles in the leg in humans remains poorly understood. Using transcranial magnetic stimulation over the leg representation of the primary motor cortex, we constructed motor evoked potential (MEP) recruitment curves to measure the resting motor threshold (RMT), maximum MEP amplitude (MEP-max), and slope in the biceps femoris, rectus femoris, tibialis anterior, soleus, and a foot muscle (i.e., abductor hallucis) in intact humans. We found that the RMT was lower and the MEP-max and slope were larger in the abductor hallucis compared with most other muscles tested. In contrast, the RMT was higher and the MEP-max and slope were lower in the biceps femoris compared to all other muscles tested. Corticospinal responses in the rectus femoris, tibialis anterior, and soleus were in between those obtained from other leg muscles, with the soleus having a higher RMT and lower MEP-max and slope than the rectus femoris and tibialis anterior. To examine the origin of increases in corticospinal excitability in the abductor hallucis, we compared short-interval intracortical inhibition (SICI) and -waves between the abductor hallucis and tibialis anterior. SICI was similar across muscles while the -wave amplitude was larger in the abductor hallucis compared with the tibialis anterior. These results support a nonuniform distribution of corticospinal output to leg muscles, highlighting that increases in corticospinal excitability in a foot muscle could be related to a spinal origin. We provide evidence on how corticospinal output differs across muscles in the leg in intact humans. We found that corticospinal responses were larger in a distal intrinsic foot muscle and were smaller in the biceps femoris compared to all other muscles in the leg. Increases in corticospinal excitability to an intrinsic foot muscle could have a spinal origin.
在非人类灵长类动物的电生理学研究中，报告了初级运动皮层对远端（相对于近端）后肢肌肉的强烈皮质脊髓输出的存在。人类腿部肌肉之间皮质脊髓输出的差异程度仍知之甚少。使用经颅磁刺激初级运动皮层的腿部代表区，我们构建运动诱发电位（MEP）募集曲线来测量静息运动阈值（RMT）、最大 MEP 幅度（MEP-max）和股二头肌、股直肌、胫骨前肌、比目鱼肌和足部肌肉（即，拇展肌）的斜率。我们发现，与大多数其他测试肌肉相比，拇展肌的 RMT 较低，MEP-max 和斜率较大。相比之下，与所有其他测试肌肉相比，股二头肌的 RMT 较高，MEP-max 和斜率较低。股直肌、胫骨前肌和比目鱼肌的皮质脊髓反应介于其他腿部肌肉获得的反应之间，比目鱼肌的 RMT 高于股直肌和胫骨前肌，而 MEP-max 和斜率则低于股直肌和胫骨前肌。为了检查拇展肌皮质脊髓兴奋性增加的起源，我们比较了拇展肌和胫骨前肌之间的短程抑制（SICI）和-波。肌肉之间的 SICI 相似，而拇展肌的-波幅度大于胫骨前肌。这些结果支持皮质脊髓输出到腿部肌肉的非均匀分布，突出表明足部肌肉皮质脊髓兴奋性的增加可能与脊髓起源有关。我们提供了关于在完整人体中腿部肌肉之间皮质脊髓输出差异的证据。我们发现，与腿部的所有其他肌肉相比，远端内在足部肌肉的皮质脊髓反应更大，而股二头肌的皮质脊髓反应更小。内在足部肌肉皮质脊髓兴奋性的增加可能具有脊髓起源。
