The effect of transcranial direct current stimulation on syntactic processing in aphasia

There are studies that investigated the effects of tDCS on linguistic abilities both in healthy and aphasic individuals. tDCS studies in aphasic individuals revealed positive effects on linguistic abilities based on the cerebral area of stimulation and conditions. The aim of the current study was to evaluate the effect of tDCS on syntactic processing by activating or supressing Wernicke's area in anodal and cathodal conditions. 10 individuals with aphasia participated in the study. All aphasic indiviuals were administered the Test of Language Assessment in Aphasia. In the beginning of each session we applied our linguistic task via a computer program that consisted of 20 target sentences, which were formed of four different syntactic structures with varying complexities. This task measured the true/false scores, reaction times, and the distractor use by aphasic individuals. After the linguistic task, each participant was subjected to 2mA tDCS for 20 minutes. In the anodal condition we applied tDCS on the left Wernicke's area (CP5), while in the cathodal stimulation we applied tDCS on right the homologue area for Wernicke (CP6). Immediately after the tDCS session, participants were subjected to the linguistic task once again. Five consecutive sessions were conducted in a period of one week. The results of the study revealed that Anodal-tDCS may improve language skills by decreasing bilateral activation whereas Cathodal-tDCS was ineffective on syntactic processing and had a negative effect on certain syntactic structures. Key words: Syntactic processing, aphasia, tDCS, neurolinguistics, language disorder