Al'joboori Yazi, Hannah Ricci, Lenham Francesca, Borgas Pia, Kremers Charlotte J P, Bunday Karen L, Rothwell John, Duffell Lynsey D
Department of Medical Physics & Biomedical Engineering, University College London, London, United Kingdom.
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, United Kingdom.
Front Neurosci. 2021 Oct 21;15:749042. doi: 10.3389/fnins.2021.749042. eCollection 2021.
Rehabilitative interventions involving electrical stimulation show promise for neuroplastic recovery in people living with Spinal Cord Injury (SCI). However, the understanding of how stimulation interacts with descending and spinal excitability remain unclear. In this study we compared the immediate and short-term (within a few minutes) effects of pairing Transcranial Magnetic Stimulation (TMS) with transcutaneous Spinal Cord stimulation (tSCS) and Peripheral Nerve Stimulation (PNS) on Corticospinal excitability in healthy subjects. Three separate experimental conditions were assessed. In Experiment I, paired associative stimulation (PAS) was applied, involving repeated pairing of single pulses of TMS and tSCS, either arriving simultaneously at the spinal motoneurones (PAS) or slightly delayed (PAS). Corticospinal and spinal excitability, and motor performance, were assessed before and after the PAS interventions in 24 subjects. Experiment II compared the immediate effects of tSCS and PNS on corticospinal excitability in 20 subjects. Experiment III compared the immediate effects of tSCS with tSCS delivered at the same stimulation amplitude but modulated with a carrier frequency (in the kHz range) on corticospinal excitability in 10 subjects. Electromyography (EMG) electrodes were placed over the Tibialis Anterior (TA) soleus (SOL) and vastus medialis (VM) muscles and stimulation electrodes (cathodes) were placed on the lumbar spine (tSCS) and lateral to the popliteal fossa (PNS). TMS over the primary motor cortex (M1) was paired with tSCS or PNS to produce Motor Evoked Potentials (MEPs) in the TA and SOL muscles. Simultaneous delivery of repetitive PAS (PAS) increased corticospinal excitability and H-reflex amplitude at least 5 min after the intervention, and dorsiflexion force was increased in a force-matching task. When comparing effects on descending excitability between tSCS and PNS, a subsequent facilitation in MEPs was observed following tSCS at 30-50 ms which was not present following PNS. To a lesser extent this facilitatory effect was also observed with HF- tSCS at subthreshold currents. Here we have shown that repeated pairing of TMS and tSCS can increase corticospinal excitability when timed to arrive simultaneously at the alpha-motoneurone and can influence functional motor output. These results may be useful in optimizing stimulation parameters for neuroplasticity in people living with SCI.
涉及电刺激的康复干预措施显示出有望帮助脊髓损伤（SCI）患者实现神经可塑性恢复。然而，对于刺激如何与下行和脊髓兴奋性相互作用的理解仍不明确。在本研究中，我们比较了在健康受试者中，将经颅磁刺激（TMS）与经皮脊髓刺激（tSCS）及外周神经刺激（PNS）配对后的即时和短期（几分钟内）对皮质脊髓兴奋性的影响。评估了三种不同的实验条件。在实验I中，应用了配对联想刺激（PAS），包括将TMS的单脉冲与tSCS重复配对，二者要么同时到达脊髓运动神经元（PAS），要么稍有延迟（PAS）。在24名受试者中，在PAS干预前后评估了皮质脊髓和脊髓兴奋性以及运动表现。实验II比较了tSCS和PNS对20名受试者皮质脊髓兴奋性的即时影响。实验III比较了tSCS与以相同刺激幅度但用载波频率（kHz范围）调制的tSCS对10名受试者皮质脊髓兴奋性的即时影响。肌电图（EMG）电极置于胫骨前肌（TA）、比目鱼肌（SOL）和股内侧肌（VM）上，刺激电极（阴极）置于腰椎（tSCS）和腘窝外侧（PNS）。对初级运动皮层（M1）进行TMS并与tSCS或PNS配对，以在TA和SOL肌肉中产生运动诱发电位（MEP）。重复PAS（PAS）的同时给药在干预后至少5分钟增加了皮质脊髓兴奋性和H反射幅度，并且在力量匹配任务中背屈力增加。当比较tSCS和PNS对下行兴奋性的影响时，在30 - 50毫秒时观察到tSCS后MEP有后续促进作用，而PNS后未出现这种情况。在亚阈值电流下，高频tSCS也在较小程度上观察到了这种促进作用。我们在此表明，当TMS和tSCS定时同时到达α运动神经元时，重复配对可增加皮质脊髓兴奋性并能影响功能性运动输出。这些结果可能有助于优化SCI患者神经可塑性的刺激参数。
