Graduate School of Health, Discipline of Physiotherapy, University of Technology Sydney, PO Box 123, Broadway, Sydney, NSW, 2007, Australia.
Department of Exercise Sciences, University of Auckland, Auckland, New Zealand.
Exp Brain Res. 2020 Nov;238(11):2531-2538. doi: 10.1007/s00221-020-05887-8. Epub 2020 Aug 30.
Transcranial magnetic stimulation (TMS) produces motor-evoked potentials (MEP) used to infer changes in corticomotor excitability. In humans, neck rotation can probe reticulospinal input on corticomotor output. This study investigated the effect of neck rotation on MEP duration in a proximal and distal upper limb muscle and compared responses between rest and preactivation. Single-pulse TMS to motor cortex was used to evoke MEPs at two stimulus intensities in 18 healthy adults (20-40 years). Surface electromyography recorded MEPs from the non-dominant biceps brachii (BB) and first dorsal interosseous (FDI). Participants were seated with the target muscle at rest or 10% preactivated, and head rotated ipsilateral, contralateral, or in neutral position. The primary outcome was MEP tail, defined as the mean difference in MEP duration between active and rest trials. Secondary outcomes were MEP duration and amplitude. MEP tail was modulated by neck rotation in the proximal BB (P = 0.03) but not distal FDI (P > 0.19), with shorter duration during ipsilateral or contralateral rotation relative to neutral. In a neutral neck position, MEP duration was prolonged by muscle preactivation and higher TMS intensities in the FDI and BB (P < 0.03). Neck rotation attenuated the prolongation of MEP duration during preactivation in the BB, but not the FDI. Neck rotation had no effect on MEP amplitude for either muscle (P > 0.05). Modulation of the late portion of the MEP by rotation of the neck could indicate subcortical projections to alpha-motoneuron pools are stronger in proximal than distal upper limb muscles. These findings may have relevance for using MEP duration as a neural biomarker in neurological diseases.
经颅磁刺激（TMS）产生运动诱发电位（MEP），用于推断皮质运动兴奋性的变化。在人类中，颈部旋转可以探测到网状脊髓传入对皮质运动输出的影响。本研究调查了颈部旋转对近端和远端上肢肌肉 MEP 持续时间的影响，并比较了静息和预激活状态下的反应。使用单脉冲 TMS 刺激运动皮层，在 18 名健康成年人（20-40 岁）中以两种刺激强度诱发出 MEP。表面肌电图记录非优势肱二头肌（BB）和第一背侧骨间肌（FDI）的 MEP。参与者坐在座位上，目标肌肉处于静息或 10%预激活状态，头向同侧、对侧或中立位旋转。主要结局是 MEP 尾巴，定义为主动和静息试验之间 MEP 持续时间的平均差异。次要结局是 MEP 持续时间和幅度。MEP 尾巴受颈部旋转的调节，在近端 BB（P=0.03）但不在远端 FDI（P>0.19），相对于中立位，同侧或对侧旋转时持续时间更短。在中立位颈部位置，FDI 和 BB 中的肌肉预激活和更高的 TMS 强度延长了 MEP 持续时间（P<0.03）。颈部旋转减弱了 BB 中预激活期间 MEP 持续时间的延长，但 FDI 中没有（P>0.05）。颈部旋转对两种肌肉的 MEP 幅度均无影响（P>0.05）。颈部旋转对 MEP 后期部分的调制可能表明，与远端上肢肌肉相比，近端上肢肌肉的皮质下投射到α运动神经元池更强。这些发现可能与将 MEP 持续时间用作神经疾病的神经生物标志物有关。
