Putting focus on transcranial direct current stimulation in language production studies

Objective Previous language production studies targeting the inferior frontal and superior temporal gyrus using anodal tDCS have provided mixed results. Part of this heterogeneity may be explained by limited target region focality of conventionally used electrode montages. We examined the focality of conventionally and alternative electrode montages. Methods Electrical field distributions of anodal tDCS targeting IFG and pSTG were simulated in conventional setups (anodal electrode over IFG/pSTG, reference electrode over right supraorbital region) and an alternative electrode montage in four different brains. Results Conventional montages showed maximum field strengths outside of the target regions. Results from alternative electrode montages showed that focality of tDCS could be improved by adjustments in electrode size and placement. Conclusions Heterogeneity of findings of language production studies deploying conventional tDCS montages may in part be explained by diffuse electrical field distributions. Alternative montages may improve focality and provide more unequivocal results. Significance Reliability of tDCS in language production research, both in basic and applied fields, can be improved by adopting different electrode montages which target the region of interest in a more direct way.