AUTHOR=Meinzer Marcus , Shahbabaie Alireza , Antonenko Daria , Blankenburg Felix , Fischer Rico , Hartwigsen Gesa , Nitsche Michael A. , Li Shu-Chen , Thielscher Axel , Timmann Dagmar , Waltemath Dagmar , Abdelmotaleb Mohamed , Kocataş Harun , Caisachana Guevara Leonardo M. , Batsikadze Giorgi , Grundei Miro , Cunha Teresa , Hayek Dayana , Turker Sabrina , Schlitt Frederik , Shi Yiquan , Khan Asad , Burke Michael , Riemann Steffen , Niemann Filip , Flöel Agnes TITLE=Investigating the neural mechanisms of transcranial direct current stimulation effects on human cognition: current issues and potential solutions JOURNAL=Frontiers in Neuroscience VOLUME=18 YEAR=2024 URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2024.1389651 DOI=10.3389/fnins.2024.1389651 ISSN=1662-453X ABSTRACT=

Transcranial direct current stimulation (tDCS) has been studied extensively for its potential to enhance human cognitive functions in healthy individuals and to treat cognitive impairment in various clinical populations. However, little is known about how tDCS modulates the neural networks supporting cognition and the complex interplay with mediating factors that may explain the frequently observed variability of stimulation effects within and between studies. Moreover, research in this field has been characterized by substantial methodological variability, frequent lack of rigorous experimental control and small sample sizes, thereby limiting the generalizability of findings and translational potential of tDCS. The present manuscript aims to delineate how these important issues can be addressed within a neuroimaging context, to reveal the neural underpinnings, predictors and mediators of tDCS-induced behavioral modulation. We will focus on functional magnetic resonance imaging (fMRI), because it allows the investigation of tDCS effects with excellent spatial precision and sufficient temporal resolution across the entire brain. Moreover, high resolution structural imaging data can be acquired for precise localization of stimulation effects, verification of electrode positions on the scalp and realistic current modeling based on individual head and brain anatomy. However, the general principles outlined in this review will also be applicable to other imaging modalities. Following an introduction to the overall state-of-the-art in this field, we will discuss in more detail the underlying causes of variability in previous tDCS studies. Moreover, we will elaborate on design considerations for tDCS-fMRI studies, optimization of tDCS and imaging protocols and how to assure high-level experimental control. Two additional sections address the pressing need for more systematic investigation of tDCS effects across the healthy human lifespan and implications for tDCS studies in age-associated disease, and potential benefits of establishing large-scale, multidisciplinary consortia for more coordinated tDCS research in the future. We hope that this review will contribute to more coordinated, methodologically sound, transparent and reproducible research in this field. Ultimately, our aim is to facilitate a better understanding of the underlying mechanisms by which tDCS modulates human cognitive functions and more effective and individually tailored translational and clinical applications of this technique in the future.