Roumengous Thibault, Thakkar Bhushan, Peterson Carrie L
Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, United States.
Department of Physical Therapy, Virginia Commonwealth University, Richmond, VA, United States.
Front Hum Neurosci. 2022 Nov 3;16:976014. doi: 10.3389/fnhum.2022.976014. eCollection 2022.
After spinal cord injury (SCI), motoneuron death occurs at and around the level of injury which induces changes in function and organization throughout the nervous system, including cortical changes. Muscle affected by SCI may consist of both innervated (accessible to voluntary drive) and denervated (inaccessible to voluntary drive) muscle fibers. Voluntary activation measured with transcranial magnetic stimulation (VA) can quantify voluntary cortical/subcortical drive to muscle but is limited by technical challenges including suboptimal stimulation of target muscle relative to its antagonist. The motor evoked potential (MEP) in the biceps compared to the triceps (i.e., MEP ratio) may be a key parameter in the measurement of biceps VA after SCI. We used paired pulse TMS, which can inhibit or facilitate MEPs, to determine whether the MEP ratio affects VA in individuals with tetraplegia. Ten individuals with tetraplegia following cervical SCI and ten non-impaired individuals completed single pulse and paired pulse VA protocols. Paired pulse stimulation was delivered at 1.5, 10, and 30 ms inter-stimulus intervals (ISI). In both the SCI and non-impaired groups, the main effect of the stimulation pulse (paired pulse compared to single pulse) on VA was not significant in the linear mixed-effects models. In both groups for the stimulation parameters we tested, the MEP ratio was not modulated across all effort levels and did not affect VA. Linearity of the voluntary moment and superimposed twitch moment relation was lower in SCI participants compared to non-impaired. Poor linearity in the SCI group limits interpretation of VA. Future work is needed to address methodological issues that limit clinical application of VA.
脊髓损伤（SCI）后，运动神经元在损伤水平及周围发生死亡，这会引起整个神经系统功能和组织的变化，包括皮质变化。受SCI影响的肌肉可能由受神经支配（可接受自主驱动）和失神经支配（不可接受自主驱动）的肌纤维组成。经颅磁刺激（VA）测量的自主激活可以量化自主皮质/皮质下对肌肉的驱动，但受到技术挑战的限制，包括相对于其拮抗肌对目标肌肉的刺激效果欠佳。与肱三头肌相比，肱二头肌的运动诱发电位（MEP）（即MEP比率）可能是测量SCI后肱二头肌VA的关键参数。我们使用可以抑制或促进MEP的成对脉冲TMS，来确定MEP比率是否会影响四肢瘫痪个体的VA。10名颈髓损伤后四肢瘫痪的个体和10名未受损个体完成了单脉冲和成对脉冲VA方案。成对脉冲刺激在1.5、10和30毫秒的刺激间隔（ISI）下进行。在SCI组和未受损组中，刺激脉冲（成对脉冲与单脉冲相比）对VA的主要影响在线性混合效应模型中均不显著。在我们测试的刺激参数下，两组中MEP比率在所有用力水平上均未受到调节，也未影响VA。与未受损个体相比，SCI参与者的自主力矩与叠加抽搐力矩关系的线性较低。SCI组的线性较差限制了对VA的解释。需要开展进一步的工作来解决限制VA临床应用的方法学问题。
