Background: Inhibitory control refers to a central cognitive capacity involved in the interruption and correction of actions. Dysfunctions in these cognitive control processes have been identified as major maintaining mechanisms in a range of mental disorders such as ADHD, binge eating disorder, obesity, and addiction. Improving inhibitory control by transcranial direct current stimulation (tDCS) could ameliorate symptoms in a broad range of mental disorders. Objective: The primary aim of this pre-registered meta-analysis was to investigate whether inhibitory control can be improved by tDCS in healthy and clinical samples. Additionally, several moderator variables were investigated. Methods: A comprehensive literature search was performed on PubMed/MEDLINE database, Web of Science, and Scopus. To achieve a homogenous sample, only studies that assessed inhibitory control in the go-/no-go (GNG) or stop-signal task (SST) were included, yielding a total of 75 effect sizes from 45 studies. Results: Results of the meta-analysis indicate a small but significant overall effect of tDCS on inhibitory control (g ¼ 0.21) which was moderated by target and return electrode placement as well as by the task. The small effect size was further reduced after correction for publication bias. Conclusion: Based on the studies included, our meta-analytic approach substantiates previously observed differences between brain regions, i.e., involvement of the right inferior frontal gyrus (rIFG) vs. the right dorsolateral prefrontal cortex (rDLPFC) in inhibitory control. Results indicate a small moderating effect of tDCS on inhibitory control in single-session studies and highlight the relevance of technical and behavioral parameters.

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Several studies have investigated how abstract and concrete concepts are processed in the brain, but data are controversial, in particular neuroimaging data contrast with clinical neuropsychological observations. A possible explanation could be that previous meta-analyses considered different types of stimuli (nouns, verbs, literal and figurative sentences). Using the ALE method, we meta-analyzed 32 brain-activation imaging studies that considered only words (nouns and verbs). Five clusters were associated with concrete words (the left superior occipital, middle temporal, parahippocampal and bilateral posterior cingulate, angular, and precuneus gyri); four clusters were associated with abstract words (left IFG, superior, and middle temporal gyri). When only nouns were considered three left activation clusters were associated with concrete stimuli and only one with abstract nouns (left IFG). These results confirm that concrete and abstract word processing involves at least partially segregated brain areas, the IFG being relevant for abstract nouns and verbs while more posterior temporo-parieto-occipital regions seem to be crucial for concrete words.