Charalambous Charalambos C, Hadjipapas Avgis
Department of Basic and Clinical Sciences, Medical School, University of Nicosia, Nicosia, Cyprus.
Center for Neuroscience and Integrative Brain Research (CENIBRE), Medical School, University of Nicosia, Nicosia, Cyprus.
Front Syst Neurosci. 2022 Oct 28;16:922841. doi: 10.3389/fnsys.2022.922841. eCollection 2022.
Alpha and beta oscillations have been assessed thoroughly during walking due to their potential role as proxies of the corticoreticulospinal tract (CReST) and corticospinal tract (CST), respectively. Given that damage to a descending tract after stroke can cause walking deficits, detailed knowledge of how these oscillations mechanistically contribute to walking could be utilized in strategies for post-stroke locomotor recovery. In this review, the goal was to summarize, synthesize, and discuss the existing evidence on the potential differential role of these oscillations on the motor descending drive, the effect of transcranial alternate current stimulation (tACS) on neurotypical and post-stroke walking, and to discuss remaining gaps in knowledge, future directions, and methodological considerations. Electrophysiological studies of corticomuscular, intermuscular, and intramuscular coherence during walking clearly demonstrate that beta oscillations are predominantly present in the dorsiflexors during the swing phase and may be absent post-stroke. The role of alpha oscillations, however, has not been pinpointed as clearly. We concluded that both animal and human studies should focus on the electrophysiological characterization of alpha oscillations and their potential role to the CReST. Another approach in elucidating the role of these oscillations is to modulate them and then quantify the impact on walking behavior. This is possible through tACS, whose beneficial effect on walking behavior (including boosting of beta oscillations in intramuscular coherence) has been recently demonstrated in both neurotypical adults and stroke patients. However, these studies still do not allow for specific roles of alpha and beta oscillations to be delineated because the tACS frequency used was much lower (i.e., individualized calculated gait frequency was used). Thus, we identify a main gap in the literature, which is tACS studies actually stimulating at alpha and beta frequencies during walking. Overall, we conclude that for beta oscillations there is a clear connection to descending drive in the corticospinal tract. The precise relationship between alpha oscillations and CReST remains elusive due to the gaps in the literature identified here. However, better understanding the role of alpha (and beta) oscillations in the motor control of walking can be used to progress and develop rehabilitation strategies for promoting locomotor recovery.
由于α波和β波振荡分别作为皮质网状脊髓束（CReST）和皮质脊髓束（CST）的替代指标具有潜在作用，因此在步行过程中对它们进行了全面评估。鉴于中风后下行传导束受损会导致步行障碍，深入了解这些振荡如何在机械层面上对步行产生影响，可能有助于制定中风后运动恢复策略。在本综述中，目标是总结、综合并讨论现有证据，这些证据涉及这些振荡在运动下行驱动中的潜在差异作用、经颅交流电刺激（tACS）对神经正常和中风后步行的影响，并讨论知识空白、未来方向和方法学考量。对步行过程中皮质肌肉、肌肉间和肌肉内相干性的电生理研究清楚地表明，β波振荡在摆动期主要出现在背屈肌中，中风后可能消失。然而，α波振荡的作用尚未得到明确界定。我们得出结论，动物和人类研究都应关注α波振荡的电生理特征及其对CReST的潜在作用。阐明这些振荡作用的另一种方法是对它们进行调制，然后量化对步行行为的影响。这可以通过tACS实现，最近在神经正常的成年人和中风患者中均已证明tACS对步行行为具有有益影响（包括增强肌肉内相干性中的β波振荡）。然而，这些研究仍无法明确α波和β波振荡的具体作用，因为所使用的tACS频率要低得多（即使用个体化计算的步态频率）。因此，我们确定了文献中的一个主要空白，即tACS研究实际上在步行过程中以α波和β波频率进行刺激。总体而言，我们得出结论，对于β波振荡，与皮质脊髓束中的下行驱动存在明确联系。由于本文中确定的文献空白，α波振荡与CReST之间的确切关系仍然难以捉摸。然而，更好地理解α波（和β波）振荡在步行运动控制中的作用，可用于推进和制定促进运动恢复的康复策略。
