Department of Neurorehabilitation Laboratory, Graduate School of Health Sciences, Kio University, 4-2-2 Umaminaka, Koryo, Kitakatsuragi-gun, Nara, 635-0832, Japan.
Department of Therapy, Takarazuka Rehabilitation Hospital, Medical Corporation SHOWAKAI, 22-2 Tsurunoso, Takarazuka-shi, Hyogo, 665-0833, Japan.
Exp Brain Res. 2024 Oct;242(10):2381-2390. doi: 10.1007/s00221-024-06894-9. Epub 2024 Aug 12.
Cerebellar transcranial direct current stimulation (ctDCS) modulates cerebellar cortical excitability in a polarity-dependent manner and affects inhibitory pathways from the cerebellum. The cerebellum modulates spinal reflex excitability via the vestibulospinal tract and other pathways projecting to the spinal motor neurons; however, the effects of ctDCS on the excitability of spinal motor neurons and vestibulospinal tract remain unclear. The experiment involved 13 healthy individuals. ctDCS (sham-ctDCS, anodal-ctDCS, and cathodal-ctDCS) was applied to the cerebellar vermis at 2 mA with an interval of at least 3 days between each condition. We measured the maximal M-wave (Mmax) and maximal H-reflex (Hmax) in the right soleus muscle to assess the excitability of spinal motor neurons. We applied galvanic vestibular stimulation (GVS) for 200 ms at 100 ms before tibial nerve stimulation to measure Hmax conditioned by GVS (GVS-Hmax) and calculated the change rate of Hmax by GVS as the excitability of vestibulospinal tract. We measured the Mmax, Hmax, and GVS-Hmax before, during, and after ctDCS in the sitting posture. No main effects of tDCS condition, main effects of time, or interaction effects were observed in Hmax/Mmax or the change rate of Hmax by GVS. It has been suggested that ctDCS does not affect the excitability of spinal motor neurons and vestibulospinal tract, as measured by neurophysiological methods, such as the H-reflex, in healthy individuals in a sitting posture. Effect of ctDCS on other descending pathways to spinal motor neurons, the neurological mechanism of tDCS and the cerebellar activity during the experiment may have contributed to these results. Therefore, we need to investigate the involvement of the cerebellum in Hmax/Mmax and the change rate of Hmax by GVS under different neuromodulation techniques and postural conditions.
小脑经颅直流电刺激（ctDCS）以极性依赖的方式调节小脑皮质兴奋性，并影响来自小脑的抑制性通路。小脑通过前庭脊髓束和投射到脊髓运动神经元的其他途径调节脊髓反射兴奋性；然而，ctDCS 对脊髓运动神经元和前庭脊髓束兴奋性的影响尚不清楚。该实验涉及 13 名健康个体。ctDCS（假刺激-ctDCS、阳极刺激-ctDCS 和阴极刺激-ctDCS）以 2 mA 施加于小脑蚓部，每种条件之间至少间隔 3 天。我们测量右侧比目鱼肌的最大 M 波（Mmax）和最大 H 反射（Hmax），以评估脊髓运动神经元的兴奋性。我们在胫神经刺激前 100 毫秒施加电前庭刺激（GVS），测量 GVS 条件下的 Hmax（GVS-Hmax），并计算 GVS 引起的 Hmax 变化率作为前庭脊髓束的兴奋性。我们在坐姿下测量 ctDCS 前后及期间的 Mmax、Hmax 和 GVS-Hmax。在 Hmax/Mmax 或 GVS 引起的 Hmax 变化率方面，未观察到 tDCS 条件的主效应、时间的主效应或交互效应。提示 ctDCS 不会影响健康个体坐姿下神经生理方法（如 H 反射）测量的脊髓运动神经元和前庭脊髓束的兴奋性。ctDCS 对其他下行通路至脊髓运动神经元的影响、tDCS 的神经机制以及实验期间小脑的活动可能促成了这些结果。因此，我们需要在不同的神经调节技术和姿势条件下研究小脑在 Hmax/Mmax 和 GVS 引起的 Hmax 变化率中的作用。
