Attentional control over sensory processing has been linked to neural alpha oscillations and related inhibition of cerebral cortex. Despite the wide consensus on the functional relevance of alpha oscillations for attention, precise neural mechanisms of how alpha oscillations shape perception and how this top-down modulation is implemented in cortical networks remain unclear. Here, we tested the hypothesis that alpha oscillations in frontal eye fields (FEFs) are causally involved in the top-down regulation of visual processing in humans (male and female). We applied sham-controlled, intermittent transcranial alternating current stimulation (tACS) over bilateral FEF at either 10 Hz (alpha) or 40 Hz (gamma) to manipulate attentional preparation in a visual discrimination task. Under each stimulation condition, we measured psychometric functions for contrast perception and introduced a novel linear mixed modeling approach for statistical control of neurosensory side effects of the electric stimulation. tACS at alpha frequency reduced the slope of the psychometric function, resulting in improved subthreshold and impaired superthreshold contrast perception. Side effects on the psychometric functions were complex and showed large interindividual variability. Controlling for the impact of side effects on the psychometric parameters by using covariates in the linear mixed model analysis reduced this variability and strengthened the perceptual effect. We propose that alpha tACS over FEF mimicked a state of endogenous attention by strengthening a fronto-occipitoparietal network in the alpha band. We speculate that this network modulation enhanced phasic gating in occipitoparietal cortex leading to increased variability of single-trial psychometric thresholds, measurable as a reduction of psychometric slope.

对感觉处理的注意力控制与神经阿尔法振荡和大脑皮层的相关抑制有关。尽管人们对阿尔法振荡与注意力的功能相关性达成了广泛共识，但阿尔法振荡如何塑造感知以及这种自上而下的调制如何在皮质网络中实施的精确神经机制仍不清楚。在这里，我们测试了这样的假设：额叶视野 (FEF) 中的 α 振荡因果性地参与人类（男性和女性）视觉处理的自上而下的调节。我们在双侧 FEF 上以 10 Hz（α）或 40 Hz（γ）应用假控制的间歇性经颅交流电刺激 (tACS)，以操纵视觉辨别任务中的注意力准备。在每种刺激条件下，我们测量了对比感知的心理测量函数，并引入了一种新颖的线性混合建模方法，用于电刺激的神经感觉副作用的统计控制。 α 频率的 tACS 降低了心理测量函数的斜率，从而改善了阈下对比度感知并损害了阈上对比度感知。对心理测量功能的副作用很复杂，并且表现出很大的个体差异。通过在线性混合模型分析中使用协变量来控制副作用对心理测量参数的影响，减少了这种变异性并增强了感知效果。我们提出，FEF 上的 alpha tACS 通过加强 alpha 频带中的额枕顶叶网络来模拟内源性注意力状态。 我们推测，这种网络调制增强了枕顶叶皮层的相位门控，导致单次试验心理测量阈值的变异性增加，可以通过心理测量斜率的减小来测量。