Department of Clinical and Movement Neurosciences, UCL Queen Square Institute of Neurology, University College London, 33 Queen Square, London, WC1N 3BG, UK.
Department of Medical Sciences and Public Health, University of Cagliari, Cittadella Universitaria Di Monserrato, 09042, Monserrato, Cagliari, Italy.
Cerebellum. 2023 Jun;22(3):319-331. doi: 10.1007/s12311-022-01398-0. Epub 2022 Mar 30.
Understanding cerebellar-cortical physiological interactions is of fundamental importance to advance the efficacy of neurorehabilitation strategies for patients with cerebellar damage. Previous works have aimed to modulate this pathway by applying transcranial electrical or magnetic stimulation (TMS) over the cerebellum and probing the resulting changes in the primary motor cortex (M1) excitability with motor-evoked potentials (MEPs). While these protocols produce changes in cerebellar excitability, their ability to modulate MEPs has produced inconsistent results, mainly due to the MEP being a highly variable outcome measure that is susceptible to fluctuations in the excitability of M1 neurons and spinal interneurons. To overcome this limitation, we combined TMS with electroencephalography (EEG) to directly record TMS-evoked potentials (TEPs) and oscillations from the scalp. In three sessions, we applied intermittent theta-burst stimulation (iTBS), cathodal direct current stimulation (c-DC) or sham stimulation to modulate cerebellar activity. To assess the effects on M1 and nearby cortex, we recorded TMS-EEG and MEPs before, immediately after (T1) and 15 min (T2) following cerebellar neuromodulation. We found that cerebellar iTBS immediately increased TMS-induced alpha oscillations and produced lasting facilitatory effects on TEPs, whereas c-DC immediately decreased TMS-induced alpha oscillations and reduced TEPs. We also found increased MEP following iTBS but not after c-DC. All of the TMS-EEG measures showed high test-retest repeatability. Overall, this work importantly shows that cerebellar neuromodulation influences both cortical and corticospinal physiological measures; however, they are more pronounced and detailed when utilizing TMS-EEG outcome measures. These findings highlight the advantage of using TMS-EEG over MEPs when assessing the effects of neuromodulation.
理解小脑-皮质的生理相互作用对于提高小脑损伤患者神经康复策略的效果至关重要。以前的工作旨在通过在小脑上施加经颅电或磁刺激（TMS）并探测由此产生的运动诱发电位（MEPs）来改变初级运动皮层（M1）的兴奋性来调节这条途径。虽然这些方案会改变小脑的兴奋性，但它们调节 MEPs 的能力产生了不一致的结果，主要是因为 MEP 是一个高度可变的结果测量指标，容易受到 M1 神经元和脊髓中间神经元兴奋性波动的影响。为了克服这一限制，我们将 TMS 与脑电图（EEG）结合起来，直接记录头皮上的 TMS 诱发电位（TEP）和振荡。在三个疗程中，我们施加间歇性 theta 爆发刺激（iTBS）、阴极直流电刺激（c-DC）或假刺激以调节小脑活动。为了评估对 M1 和附近皮质的影响，我们在小脑神经调节前后（T1）和 15 分钟（T2）记录 TMS-EEG 和 MEPs。我们发现小脑 iTBS 立即增加 TMS 诱导的 alpha 振荡，并对 TEP 产生持久的促进作用，而 c-DC 立即降低 TMS 诱导的 alpha 振荡并降低 TEP。我们还发现 iTBS 后 MEP 增加，但 c-DC 后没有。所有 TMS-EEG 测量都具有高度的测试-再测试可重复性。总的来说，这项工作重要地表明，小脑神经调节会影响皮质和皮质脊髓的生理测量；然而，当使用 TMS-EEG 结果测量时，它们更加明显和详细。这些发现强调了在评估神经调节效果时使用 TMS-EEG 而不是 MEPs 的优势。
