Examining the effects of non-invasive brain stimulation over Broca’s area on semantic judgement performance in adults

The current study aimed to investigate the effects of anodal transcranial direct current stimulation (tDCS) over Broca’s area (BA) on semantic judgment accuracy in a picture-word interference (PWI) task using a Go-No-go response-modality, in healthy adults. Based on previous evidence highlighting the role of BA in integrating lexical and visual information in preparation of verbal response, we hypothesized that active stimulation over BA will improve Go-response accuracy and improve RTs (primary outcome measure) to semantically congruent stimuli (Go-response condition) versus the sham-stimulation condition (control group), from pre to post tDCS intervention. To further support BA tDCS effects on attentional control mechanisms involving lexical processing control, we also predicted that active tDCS will improve inhibitory control function noted by Stroop task performance (secondary outcome measure), as indicated by improved performance on a simple Stroop task administered before and after tDCS versus control group. 40 healthy native Hebrew speakers aged 25–50 years were randomly assigned to either an active or sham tDCS stimulation group in a double-blind, sham-controlled design.  The findings indicated significant changes in accuracy and RTs in both groups from pre to post of BA- tDCS, however no significant differences were found between the groups in accuracy or in RTs fom pre to post tDCS intervetion. In conclusion, BA-tDCS was not more effective than sham conditions in improving semantic integration performance or inhibitory control from pre to post tDCS intervention.  BA-tDCS may not be directly related to inhibitory control and semantic congruency "go-response" recognition, and may indirectly facilitate attentional-control needed to allow positive practice effects on performance in healthy adult individuals over time. Further research should investigate larger healthy samples, specific clinical samples with localized BA-PFC damage, neuroimaging data collection, and multisession tDCS interventions to detect significant BA-tDCS effects on semantic integration performance over time.