Anodal transcranial direct current stimulation (tDCS), applied over the left dorsolateral prefrontal cortex (lDLPFC), can produce significant effects on working memory (WM) performance and associated neurophysiological activity. However, results from previous studies are inconsistent and occasionally contradictory. This inconsistency may be attributed to methodological and individual differences during experiments. This study therefore investigated two hypotheses: (1) A multichannel-optimized montage was expected to be more effective than a classical bipolar montage, because of increased focality. (2) The subjects were expected to benefit differently from the stimulation depending on their initial task performance. In a sham-controlled crossover study, 24 healthy participants received bipolar, multichannel, and sham stimulation for 20 min in randomized order, targeting the lDLPFC while performing a 2-back WM task. After stimulation, electroencephalography (EEG) was recorded at rest and during 2-back and nontarget continuous performance task (CPT) performance. Bipolar and multichannel stimulations were both well tolerated and effectively blinded. We found no effect of stimulation on behavioral performance or neuronal oscillations comparing the classical bipolar or multichannel montage with sham stimulation. We did, however, find an interaction between stimulation and initial task performance. For multichannel stimulation, initially low-performing participants tended to improve their WM performance while initially high-performing participants tended to worsen their performance compared to sham stimulation. Both tDCS montages induced changes in neural oscillatory power, which correlated with baseline performance. The worse the participants’ initial WM performance was, the more task-related theta power was induced by multichannel and bipolar stimulation. The same effect was observed for alpha power in the nontarget task following multichannel stimulation. Notably, we were not able to show a superiority of multichannel stimulation compared to bipolar stimulation. Still, comparing both montages with sham stimulation, multichannel stimulation led to stronger effects than bipolar stimulation. The current study highlights the importance of investigating different parameters with potential influence on tDCS effects in combination. Our results demonstrate how individual differences in cognitive performance and electrode montages influence effects of tDCS on neuropsychological performance. These findings support the idea of an individualized and optimized stimulation setting, potentially leading to increased tDCS effects.

中文翻译：

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单个基线性能和电极蒙太奇对左侧背外侧前额叶皮层阳极 tDCS 影响的影响

应用于左背外侧前额叶皮层 (lDLPFC) 的阳极经颅直流电刺激 (tDCS) 可以对工作记忆 (WM) 性能和相关的神经生理活动产生显着影响。然而，先前研究的结果不一致，有时相互矛盾。这种不一致可能归因于实验过程中的方法和个体差异。因此，本研究调查了两个假设：（1）多通道优化蒙太奇预计比经典双极蒙太奇更有效，因为焦点增加。(2) 根据他们最初的任务表现，预期受试者从刺激中获益不同。在一项假对照交叉研究中，24 名健康参与者接受了双极、多通道、和以随机顺序进行 20 分钟的假刺激，在执行 2-back WM 任务时针对 lDLPFC。刺激后，记录休息和 2-back 和非目标连续表现任务 (CPT) 表现期间的脑电图 (EEG)。双极和多通道刺激均具有良好的耐受性并且有效地失明。将经典双极或多通道蒙太奇与假刺激进行比较，我们发现刺激对行为表现或神经元振荡没有影响。然而，我们确实发现了刺激和初始任务表现之间的相互作用。对于多通道刺激，与假刺激相比，最初表现不佳的参与者倾向于提高他们的 WM 表现，而最初表现出色的参与者往往会恶化他们的表现。两种 tDCS 蒙太奇都诱导了神经振荡功率的变化，这与基线性能相关。参与者的初始 WM 表现越差，多通道和双极刺激引起的与任务相关的 theta 功率就越多。在多通道刺激后的非目标任务中观察到相同的效果。值得注意的是，与双极刺激相比，我们无法展示多通道刺激的优越性。尽管如此，将两种蒙太奇与假刺激进行比较，多通道刺激比双极刺激产生更强的效果。当前的研究强调了研究对 tDCS 效应有潜在影响的不同参数的重要性。我们的结果证明了认知表现和电极蒙太奇的个体差异如何影响 tDCS 对神经心理表现的影响。这些发现支持个性化和优化刺激设置的想法，可能会导致 tDCS 效应增加。