Research trends and knowledge mapping of transcranial direct current stimulation in depression: a bibliometric study based on web of science, Scopus, and PubMed (2000-2025).

Background: Depressive disorders are clinically heterogeneous and mechanistically complex psychiatric conditions. Transcranial direct current stimulation (tDCS), a key non-invasive neuromodulation technique, has expanded rapidly in both therapeutic application and mechanistic research. However, the field is marked by rapid publication growth, thematic diversity, and variability in evidence quality. A systematic quantitative synthesis is therefore needed to map the research landscape, identify hotspots, and inform future directions. Methods: A systematic search was conducted for English-language publications in the Web of Science Core Collection (WoSCC), Scopus, and PubMed using the terms ("Transcranial direct current stimulation" OR "tDCS") AND ("depression" OR "major depressive disorder" OR "depressive disorder" OR "MDD"). Only articles and reviews were included. Records from 2026 and non-research publications, including conference abstracts, editorials, letters, news items, and errata, were excluded. Deduplication was performed using DOI-based matching followed by title-assisted matching. Bibliometrix (R), VOSviewer, and CiteSpace were used to analyze publication trends, contributions by countries/regions, institutions, authors, and journals, collaboration networks, keyword co-occurrence, thematic clustering, and burst terms. Citation analysis was based on WoSCC data only. Results: Research on tDCS for depression showed sustained growth, with marked acceleration after 2020 and a peak in 2024. The United States, Germany, and Brazil occupied central positions in both productivity and international collaboration, with the United States ranking first in publication volume. Major research hubs included the Universidade de São Paulo, the University of Toronto, and Harvard University, while Brain Stimulation, Journal of Affective Disorders, and Frontiers in Psychiatry were the leading publication venues. Highly cited studies mainly focused on neurophysiological mechanisms, pivotal randomized controlled trials, and evidence-based guidelines. Keyword analyses indicated a shift from early attention to cortical excitability, safety, and short-term efficacy toward a more integrated framework involving prefrontal-targeted stimulation, cognitive function, functional connectivity, treatment outcomes, and cross-disorder applications. Conclusion: tDCS research in depression is entering a multidimensional and interdisciplinary phase, with increasing emphasis on network-level mechanisms and precision intervention. Functional connectivity is emerging as a potential biomarker for patient stratification and outcome prediction. Further progress depends on multicenter standardization, reproducible analytic pipelines, and high-quality comparative effectiveness research.