4.4. Network-level
CORTEX
In line with our hypothesis, significant dose-response relationships were observed at the network level, highlighting the importance of examining global network effects rather than local associations found in voxel-level, ROI-level, or cluster-level approaches. Specifically, we observed a significant positive correlation between task-based frontoparietal functional connectivity and EF intensity within the prefrontal cortex. These findings align with previous research conducted by Indahlastria et al. during a working memory task, where they reported a significant correlation between current density values in DLPFC and changes in task-based functional connectivity within the working memory network in older adults [Two main points should be highlighted based on our results. Firstly, our findings demonstrated significant associations exclusively at the network level, indicating that the neurobiological effects of tDCS may not manifest in a straightforward manner at the voxel, region, or cluster level. This emphasizes the significance of examining network-level changes during stimulation. In recent years, there has been a growing emphasis on network-based effects of brain stimulation technologies, and our results further support the notion that tDCS effects are likely to spread across networks rather than being confined to specific local brain regions. Our network-level analysis sheds light on the significant modulatory effects of EFs on functional connectivity within the brain. These findings support the growing emphasis on network-level changes during tDCS and provide insights into the complexity of EF-induced effects on network dynamics. Further investigations should explore the underlying mechanisms of these network-level effects and consider the broader implications for understanding the functional consequences of tDCS.