Alvarado-Navarrete Mónica Del Carmen, Pliego-Carrillo Adriana C, Ledesma-Ramírez Claudia Ivette, Cuellar Carlos A
Biomedical Engineering, School of Medicine, Autonomous University of the State of Mexico, Toluca, Mexico.
School of Sport Sciences, Universidad Anáhuac México, Huixquilucan, Mexico.
Front Integr Neurosci. 2023 Aug 30;17:1234613. doi: 10.3389/fnint.2023.1234613. eCollection 2023.
The comprehension of the neural elements interacting in the spinal cord affected by vestibular input will contribute to the understanding of movement execution in normal and pathological conditions. In this context, Hoffman's reflex (H-reflex) has been used to evaluate transient excitability changes on the spinal cord descending pathways. The post-activation depression (P-AD) of the H-reflex consists of evoking consecutive responses (>1 Hz) provoking an amplitude depression, which has been shown to diminish in pathological conditions (i.e., spasticity, diabetic neuropathy). Galvanic Vestibular Stimulation (GVS) is a non-invasive method that activates the vestibular afferents and has been used to study the excitability of the H-reflex applied as a conditioning pulse. To our knowledge, there are no reports evaluating the P-AD during and after GVS. Our primary aim was to determine if GVS alters the P-AD evoked by stimulating the tibial nerve at 0.1, 1, 5, and 10 Hz, recording in the gastrocnemius and soleus muscles. Direct current stimulation of 2.0 ± 0.6 mA with the cathode ipsilateral (Ipsi) or contralateral (Contra) to the H-reflex electrode montage was applied bilaterally over the mastoid process in 19 healthy subjects. The P-AD's immediate post-GVS response (P Ipsi, P Contra) was also analyzed. Secondarily, we analyzed the excitability of the H-reflex during GVS. Responses evoked at 0.1 Hz with GVS, post-GVS, and a Control (no GVS) condition were used for comparisons. Our results show that P-AD persisted in all subjects despite increased excitability induced by GVS: statistical significance was found when comparing P-AD at 1, 5, and 10 Hz with the corresponding condition (Control, Ipsi, P Ipsi, Contra, P Contra) at 0.1 Hz ( < 0.001). Additionally, the increase in excitability produced by GVS was quantified for the first H-reflex of each P-AD stimulation frequency. The percentage change for all GVS conditions surpassed the Control by at least 20%, being statistically significant for Contra compared to Control ( < 0.01). In summary, although GVS increases the excitability of the vestibulospinal pathway at a premotor level, the neural inhibitory mechanism present in P-AD remains unaltered in healthy subjects.
理解受前庭输入影响的脊髓中相互作用的神经元件，将有助于理解正常和病理状态下的运动执行。在此背景下，霍夫曼反射（H反射）已被用于评估脊髓下行通路的瞬时兴奋性变化。H反射的激活后抑制（P-AD）包括诱发连续反应（>1Hz）并导致幅度降低，已证明在病理状态（即痉挛、糖尿病性神经病变）下这种降低会减弱。电前庭刺激（GVS）是一种激活前庭传入神经的非侵入性方法，已被用于研究作为条件脉冲应用时H反射的兴奋性。据我们所知，尚无关于GVS期间及之后评估P-AD的报道。我们的主要目的是确定GVS是否会改变在0.1、1、5和10Hz刺激胫神经时诱发的P-AD，并在腓肠肌和比目鱼肌中进行记录。对19名健康受试者双侧乳突施加2.0±0.6mA的直流电刺激，阴极与H反射电极组合同侧（Ipsi）或对侧（Contra）。还分析了GVS后立即出现的P-AD反应（P Ipsi、P Contra）。其次，我们分析了GVS期间H反射的兴奋性。将GVS时、GVS后以及对照（无GVS）条件下以0.1Hz诱发的反应用于比较。我们的结果表明，尽管GVS诱导兴奋性增加，但所有受试者的P-AD均持续存在：将1、5和10Hz时的P-AD与0.1Hz时的相应条件（对照、Ipsi、P Ipsi、Contra、P Contra）进行比较时发现有统计学意义（<0.001）。此外，针对每个P-AD刺激频率的第一个H反射，对GVS产生的兴奋性增加进行了量化。所有GVS条件下的百分比变化比对照至少高出20%，与对照相比，Contra具有统计学意义（<0.01）。总之，尽管GVS在运动前水平增加了前庭脊髓通路的兴奋性，但健康受试者中P-AD中存在的神经抑制机制保持不变。
