Transcranial Direct Current Stimulation Effects on Semantic Processing in Healthy Individuals

• Studies have reported that tDCS can modulate specific aspects of semantic processing in healthy subjects.
• Results from tDCS studies indicate that the frontal, temporal and parietal cortices are involved in semantic processing.
• tDCS contributes at characterizing the functional roles of brain regions involved in semantic processing (e.g., processing salient or distant meanings).

BackgroundSemantic processing allows us to use conceptual knowledge about the world. It has been associated with a large distributed neural network that includes the frontal, temporal and parietal cortices. Recent studies using transcranial direct current stimulation (tDCS) also contributed at investigating semantic processing.Objective/hypothesesThe goal of this article was to review studies investigating semantic processing in healthy individuals with tDCS and discuss findings from these studies in line with neuroimaging results. Based on functional magnetic resonance imaging studies assessing semantic processing, we predicted that tDCS applied over the inferior frontal gyrus, middle temporal gyrus, and posterior parietal cortex will impact semantic processing.MethodsWe conducted a search on Pubmed and selected 27 articles in which tDCS was used to modulate semantic processing in healthy subjects. We analysed each article according to these criteria: demographic information, experimental outcomes assessing semantic processing, study design, and effects of tDCS on semantic processes.ResultsFrom the 27 reviewed studies, 8 found main effects of stimulation. In addition to these 8 studies, 17 studies reported an interaction between stimulus types and stimulation conditions (e.g. incoherent functional, but not instrumental, actions were processed faster when anodal tDCS was applied over the posterior parietal cortex as compared to sham tDCS). Results suggest that regions in the frontal, temporal, and parietal cortices are involved in semantic processing.ConclusionstDCS can modulate some aspects of semantic processing and provide information on the functional roles of brain regions involved in this cognitive process.