NETWORK-BASED TACS MODULATES PRESTIMULUS EEG ALPHA ACTIVITY DURING COHERENT MOTION PERCEPTION​

Transcranial alternating current stimulation (tACS) is a promising non-invasive tool for cognitive neuromodulation, though its effects on coherent motion perception remain inconclusive. This study investigated the differential neuromodulatory effects of tACS on behavioral responses and electrophysiological patterns (theta and alpha bands) during a random-dot kinematogram (RDK) task with varying motion coherence (25%, 50%, 75%). TACS was applied to either an anterior (dACC, right anterior insula) or a posterior network (superior parietal lobule, right visual cortex). Participants in the most difficult condition (25% coherence) were divided into subgroups based on pre-tACS accuracy. Poor-performers showed significantly reduced reaction times (RTs) and pronounced accuracy improvements following both anterior and posterior tACS (e.g., Posterior RT: Z = -2.650, p < 0.05; Accuracy: Z = 2.752, p < 0.01). In contrast, good-performers only exhibited reduced RTs during anterior tACS (Z = -2.178, p < 0.05), with no accuracy change. Electrophysiologically, poor-performers consistently showed significantly increased prestimulus EEG alpha power in the right occipitoparietal region after both anterior and posterior stimulation (Z = 1.936, p < 0.05). Good-performers exhibited no significant tACS-mediated EEG power changes. This study demonstrates that network-level tACS enhances behavioral performance and prestimulus alpha power, particularly in poor-performers struggling with the difficult coherence condition. Our findings underscore the potential of tACS as a powerful, performance-dependent tool for modulating coherent motion perception.