Transcranial direct current stimulation (tDCS) is a widely-used tool to induce neuroplasticity and modulate cortical function by applying weak direct current over the scalp. In this review, we first introduce the underlying mechanism of action, the brief history from discovery to clinical scientific research, electrode positioning and montages, and parameter setup of tDCS. Then, we review tDCS application in clinical samples including people with drug addiction, major depression disorder, Alzheimer's disease, as well as in children. This review covers the typical characteristics and the underlying neural mechanisms of tDCS treatment in such studies. This is followed by a discussion of safety, especially when the current intensity is increased or the stimulation duration is prolonged. Given such concerns, we provide detailed suggestions regarding safety procedures for tDCS operation. Lastly, future research directions are discussed. They include foci on the development of multi-tech combination with tDCS such as with TMS and fMRI; long-term behavioral and morphological changes; possible applications in other research domains, and more animal research to deepen the understanding of the biological and physiological mechanisms of tDCS stimulation.

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Aging involves cognitive decline and prominent alterations in brain activity. Electroacupuncture (EA), a traditional Chinese medicine approach, is demonstrated to be effective in improving cognitive function of older adults. However, the specific neural mechanism underlying this modulation effect remains unclear. In this study, we used functional magnetic resonance imaging (fMRI) to investigate whether EA could improve cognitive performance of community-dwelling older adults and whether these potential improvements are associated with the EA-induced brain functional connectivity alterations. Thirty healthy older adults were recruited and randomly assigned to the EA group and the control group. Behaviorally, we observed an EA-induced improvement in cognitive performance of older adults in the Montreal Cognitive Assessment. On a neural perspective, the EA intervention significantly increased the functional connectivity within the default mode network. Moreover, we found a positive association between the improvement in delayed memory performance and the alterations in the ventral medial prefrontal cortex-hippocampal formation connectivity in the EA group. This study extends previous findings by showing that healthy older adults exhibit neural plasticity manifested as increased functional connectivity after EA sessions, which could induce therapeutic effects in the treatment of neurodegenerative diseases.