Transcranial direct current stimulation in post stroke aphasia and primary progressive aphasia: Current knowledge and future clinical applications

BACKGROUND: The application of transcranial direct current stimulation (tDCS) in chronic post stroke aphasia is documented in a substantial literature, and there is some new evidence that tDCS can augment favorable language outcomes in primary progressive aphasia. Anodal tDCS is most often applied to the left hemisphere language areas to increase cortical excitability (increase the threshold of activation) and cathodal tDCS is most often applied to the right hemisphere homotopic areas to inhibit over activation in contralesional right homologues of language areas. Outcomes usually are based on neuropsychological and language test performance, following a medical model which emphasizes impairment of function, rather than a model which emphasizes functional communication. OBJECTIVE: In this paper, we review current literature of tDCS as it is being used as a research tool, and discuss future implementation of tDCS as an adjuvant treatment to behavioral speech-language pathology intervention. METHODS: We review literature describing non-invasive brain stimulation, the mechanism of tDCS, and studies of tDCS in aphasia and neurodegenerative disorders. We discuss future clinical applications. RESULTS/CONCLUSIONS: tDCS is a promising adjunct to traditional speech-language pathology intervention to address speech-language deficits after stroke and in the neurodegenerative disease, primary progressive aphasia. Limited data are available regarding how performance on these types of specific tasks translates to functional communication outcomes.