Impaired semantic categorization during transcranial direct current stimulation of the left and right inferior parietal lobule

We investigated whether semantic knowledge is organized according to domain- or feature-dimensions during a semantic categorization task. In addition, using transcranial direct current stimulation (tDCS), we assessed whether the left or right inferior parietal lobule is differentially engaged based on these dimensions. To this end, four different tDCS electrode montage groups were employed (anodal left, cathodal left, anodal right, cathodal right). Reaction times and accuracy were recorded in response to visually presented words (living and non-living concepts with a high or low number of features). In line with our expectations, living concepts elicited faster reaction times compared with non-living concepts and concepts with a high number of features elicited faster reaction times compared with concepts with a low number of features. In addition, a general, regionally and polarity-unspecific, deteriorating effect of tDCS emerged, with stimulation slowing down reaction times compared with sham. The results are discussed in the frameworks of major theories on the organization of semantic knowledge, including the Distributed Domain-Specific Hypothesis.