A Novel Approach, a Modified Phase-Based Analysis to Assess the Behavioral and Neural Effects of tDCS Across Three Brain Regions

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that has shown promise for enhancing cognitive functions such as attention and working memory, yet its effects remain inconsistent across studies. This study introduces a modified phase-based analysis to capture the temporal dynamics of tDCS-induced changes in both behavior and brain activity. Nineteen healthy adults performed a visual working memory task under active and sham stimulation targeting the left and right posterior parietal cortex (lPPC, rPPC) and right dorsolateral prefrontal cortex (rDLPFC). Trials were chronologically divided into Early, Middle, and Late phases to examine evolving cognitive states over time. Behavioral outcomes-hit rate and reaction time-did not differ significantly between stimulation and sham, suggesting stable performance across conditions. However, event-related potential (ERP) analyses revealed phase-dependent neural modulations: rDLPFC stimulation showed a trend toward reduced Contralateral Delay Activity (CDA) in the Early phase and enhanced P3 amplitude in the Late phase, indicating improved memory efficiency and consolidation, while lPPC stimulation tended to increase N2PC amplitude during the Early phase, reflecting enhanced attentional allocation.  These findings demonstrate that even without overt behavioral effects, tDCS can induce temporally specific neural changes. The modified phase-based analysis provides a sensitive framework for linking behavioral stability with dynamic ERP modulations, offering new insights into how tDCS influences attention and working memory across time.