After-effects of Parieto-occipital Gamma Transcranial Alternating Current Stimulation on Behavioral Performance and Neural Activity in Visuo-spatial Attention Task

Visuo-spatial attention enables selective focus on spatial locations while ignoring irrelevant stimuli, involving both endogenous and exogenous attention. Recent advancements in transcranial alternating current stimulation (tACS) have shown promise in modulating these attentional processes by targeting electrical oscillations in specific brain areas. Despite evidence of online effects of tACS on visuo-spatial attention performance, whether tACS can produce lasting after-effects on behavioral performance and neural activity remains unknown. This study explored these after-effects using a single-blind, sham-controlled, between-group design. Eighteen young healthy participants were equally divided into two groups receiving either sham or active gamma tACS at 40 Hz targeted at the right parieto-occipital region. Each participant performed a version of the Posner cueing task with EEG recording before and after the tACS intervention. The active tACS group exhibited greater reductions in reaction time compared to the sham group. These changes were not uniform across different attention types, suggesting specific enhancements in cognitive processing. EEG analyses revealed trial-type-specific modulation of event-related potentials, including amplitude and latency of N1 and P3 components, that paralleled the behavioral effects. Additionally, frequency-specific changes in oscillatory power during the cue-target interval—decreased alpha power and increased gamma power—as well as reduced long-range temporal correlations were observed more broadly across conditions. While limited by a small sample size, these preliminary findings provide convergent behavioral and electrophysiological evidence that parieto-occipital gamma tACS can induce lasting, condition-specific after-effects on visuo-spatial attentional networks. Competing Interest Statement The authors have declared no competing interest. Footnotes

Restructuring: The introduction was rewritten into a clearer, hypothesis-driven framework. The theoretical rationale for selecting 40 Hz stimulation was also moved to this section. Methodological Clarifications: ERP quantification was explicitly defined, detailing the use of mean voltage for amplitude and a fractional-area approach (FAL50) for latency within N1/P3 windows. Statistical Consolidation: All analytical procedures were consolidated into a newly dedicated "Statistical analysis" section. An *a priori* sensitivity analysis was included to justify the sample size and assess the robustness of the findings. Visual Enhancements: The stimulation schematic was updated to clearly mark electrode placements (P6 and Cz) and target regions. Figure 2 was relocated to the Results section for improved logical flow. Discussion Refinement: The discussion was streamlined for sharper focus, integrating behavioral and neural findings more effectively. The authors adopted a more cautious interpretation of the results, reflecting the small sample size and acknowledging recent literature on tACS mechanisms.