Enhancing cognitive performance with fronto-parietal transcranial alternating current stimulation.

Executive cognitive functions are essential for human life, and their age- or disease-related decline significantly impacts quality of life. Non-invasive brain stimulation (NIBS) targeting the multiple-demand or fronto-parietal network (FPN) has emerged as a promising intervention for enhancing various executive cognitive functions. However, variations in cognitive tasks and stimulation protocols across studies led to mixed results, rendering findings and conclusions incomparable. In this study, we synchronized oscillations over two main areas of the frontoparietal cognitive network, right dorsolateral prefrontal cortex (rDLPFC) and right posterior parietal cortex (rPPC), using high-definition (HD) dual-channel in-phase transcranial alternating current stimulation (tACS) at various stimulation frequencies (6 Hz, 40 Hz, sham). Participants completed a spatial attention task, a 3-back memory task, and a flanker cognitive control task while receiving tACS stimulation. Results revealed that gamma-band (40 Hz) stimulation improved response speed in the spatial attention task among younger participants but impaired response speed in the flanker task. Contrary to our initial expectations, theta-band stimulation did not affect cognition significantly. These findings highlight the specificity of cognitive enhancement through tACS and suggest that optimal stimulation targets may vary across cognitive domains, providing clinical implications for using tACS in treating cognitive deficits.