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BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) stands out as the most prevalent neurodevelopmental disorder of childhood, with global prevalence ranging from 3.4% to 7•2%. Its cognitive symptoms result from the combination of complex etiological processes encompassing genetic and environmental components. Available therapeutic approaches are associated with significant challenges such as modest efficacy or side effects. Transcranial direct current stimulation (tDCS) is a promising tool for enhancing cognitive performance in neuropsychiatric disorders. Trials investigating its applicability in ADHD have showed propitious, however, still preliminary findings. METHODS: We performed a systemic review by searching on Medline, Cochrane Library, Web of Science, ScienceDirect and Embase using the descriptors: "attention-deficit/hyperactivity disorder" or "ADHD"; and "transcranial direct current stimulation" or "tDCS"; following PRISMA guidelines. RESULTS: A total of 383 articles were identified. After removing duplicates, 45 studies were assessed for eligibility, and after careful review, 11 manuscripts applying tDCS in ADHD were included. Significant improvements in attention, inhibitory control and working memory were reported, in addition to increased brain connectivity following use of active tDCS. LIMITATIONS: The main limitation was the small number of trials investigating use of tDCS in ADHD. Study methods and outcome measures were quite variable, and generally did not include long-term follow-up. CONCLUSIONS: Although the extent literature indicates promising findings, the available data remains highly preliminary. Further trials evaluating the efficacy of tDCS for ADHD, with longer follow-up, are necessary. These studies will be needed to determine the optimal protocol for clinical efficacy.

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INTRODUCTION: Auditory hallucinations are defined as experiences of auditory perceptions in the absence of a provoking external stimulus. They are the most prevalent symptoms of schizophrenia with high capacity for chronicity and refractoriness during the course of disease. The transcranial direct current stimulation (tDCS) - a safe, portable, and inexpensive neuromodulation technique - has emerged as a promising treatment for the management of auditory hallucinations. OBJECTIVE: The aim of this study is to analyze the level of evidence in the literature available for the use of tDCS as a treatment for auditory hallucinations in schizophrenia. METHODS: A systematic review was performed, searching in the main electronic databases including the Cochrane Library and MEDLINE/PubMed. The searches were performed by combining descriptors, applying terms of the Medical Subject Headings (MeSH) of Descriptors of Health Sciences and descriptors contractions. PRISMA protocol was used as a guide and the terms used were the clinical outcomes ("Schizophrenia" OR "Auditory Hallucinations" OR "Auditory Verbal Hallucinations" OR "Psychosis") searched together ("AND") with interventions ("transcranial Direct Current Stimulation" OR "tDCS" OR "Brain Polarization"). RESULTS: Six randomized controlled trials that evaluated the effects of tDCS on the severity of auditory hallucinations in schizophrenic patients were selected. Analysis of the clinical results of these studies pointed toward incongruence in the information with regard to the therapeutic use of tDCS with a view to reducing the severity of auditory hallucinations in schizophrenia. Only three studies revealed a therapeutic benefit, manifested by reductions in severity and frequency of auditory verbal hallucinations in schizophrenic patients. CONCLUSION: Although tDCS has shown promising results in reducing the severity of auditory hallucinations in schizophrenic patients, this technique cannot yet be used as a therapeutic alternative due to lack of studies with large sample sizes that portray the positive effects that have been described.