Supplementary Material for: The Potential of Transcranial Alternating Current Stimulation to Alleviate Dual-Task Gait Costs in Older Adults: Insights from a Double-Blinded Pilot Study

<b><i>Background:</i></b> The performance of an attention-demanding task while walking, i.e., dual-tasking, leads to dual-task costs (e.g., reduced gait speed) in older adults. Previous studies have shown that dual-task costs in gait are associated with future falls and cognitive decline. According to the communication through coherence hypothesis, transcranial alternating current stimulation (tACS) might help alleviate this problem. <b><i>Objective:</i></b> The aim of this study was to examine the effects of a single session of theta-tACS targeting the left fronto-parietal network (L-FPN) on dual-task walking and cognitive function compared to sham stimulation and transcranial direct current stimulation (tDCS) targeting the left dorsolateral prefrontal cortex, a node within the L-FPN. <b><i>Methods:</i></b> Twenty older adults completed a four-visit, double-blinded, within-subject, cross-over study in which usual-walking, dual-task walking, and cognitive function were evaluated before and immediately after 20 min of tACS, tDCS, or sham (order randomized) stimulation. Dual-task costs to gait speed (primary outcome) and other measures were analyzed. <b><i>Results:</i></b> The dual-task cost to gait speed tended to be lower (i.e., better) after tACS (<i>p</i> = 0.067, Cohen’s d = 0.433∼small); tDCS significantly reduced this dual-task cost (<i>p</i> = 0.012, Cohen’s d = 0.618∼medium), and sham stimulation had no effect (<i>p</i> = 0.467). tACS significantly reduced the dual-task cost to step length (<i>p</i> = 0.037, Cohen’s d = 0.502∼medium); a trend was seen after tDCS (<i>p</i> = 0.069, Cohen’s d = 0.443∼small). No statistical differences were found for other measures of gait or cognitive function. <b><i>Conclusions:</i></b> The positive effects of tACS on dual-task gait speed and step length were roughly similar to those seen with tDCS. These results suggest that tACS affects the fronto-parietal network and, similar to tDCS, tACS may improve dual-tasking. Nonetheless, to achieve larger benefits and differentiate the effects of tACS and tDCS on brain function and dual-task walking in older adults, other stimulation montages and protocols should be tested.

<b><i>研究背景：</i></b> 老年人在步行同时执行需集中注意力的任务（即双任务作业）时，会产生双任务代价（例如步速降低）。既往研究表明，步态的双任务代价与未来跌倒风险及认知衰退相关。根据相干性通信假说，经颅交流电刺激（transcranial alternating current stimulation, tACS）或可缓解该问题。<b><i>研究目的：</i></b> 本研究旨在对比单次θ节律经颅交流电刺激（theta-tACS，靶向左侧额顶网络（left fronto-parietal network, L-FPN））、假刺激，以及靶向左侧背外侧前额叶皮层（左侧额顶网络的一个节点）的经颅直流电刺激（transcranial direct current stimulation, tDCS），对双任务步行与认知功能的影响。<b><i>研究方法：</i></b> 20名老年人参与了一项四次访视、双盲、被试内交叉研究，所有受试者在接受20分钟tACS、tDCS或假刺激（刺激顺序随机化）前后，分别评估了常规步行、双任务步行及认知功能。本研究对步速的双任务代价（主要结局指标）及其他测量指标进行了分析。<b><i>研究结果：</i></b> tACS干预后，步速的双任务代价呈降低趋势（即改善效果，<i>P</i> = 0.067，科恩d值=0.433，属于小效应量）；tDCS可显著降低该双任务代价（<i>P</i> = 0.012，科恩d值=0.618，属于中等效应量），而假刺激无明显影响（<i>P</i> = 0.467）。tACS可显著降低步长的双任务代价（<i>P</i> = 0.037，科恩d值=0.502，属于中等效应量）；tDCS干预后则呈趋势性改善（<i>P</i> = 0.069，科恩d值=0.443，属于小效应量）。其余步态或认知功能测量指标均未发现统计学差异。<b><i>研究结论：</i></b> tACS对双任务步速与步长的积极效应与tDCS大致相当。上述结果表明，tACS可作用于额顶网络，且与tDCS类似，或可改善双任务作业能力。不过，为获得更显著的干预收益，并区分tACS与tDCS对老年人脑功能及双任务步行的影响，仍需测试其他刺激配置方案与实验方案。