Transcranial Direct Current Stimulation as a Tool to Induce Language Recovery in Patients with Post-Stroke Aphasia
In recent years, possible therapeutic effects of transcranial direct current stimulation (tDCS) have been widely investigated in studies dealing with different types of neural pathologies. Initially, tDCS was applied for treatment of patients with motor stroke; later on, it was introduced into studies of patients with Alzheimer’s disease, multiple sclerosis, Parkinson’s disease, schizophrenia, and post-stroke aphasia. Recent reviews of tDCS application in patients with post-stroke aphasia did not provide coherent evidence on the tDCS efficiency. There were no uniform protocols of stimulation used, patients’ selection criteria were highly divergent, and the reports of treatment outcomes varied dramatically. In this review, we will focus on the reported heterogeneity of tDCS effects, trying to disentangle its putative underpinnings rooted in the diversity of lesion types, aphasia severity, and recovery stages. Given the current theoretical models suggesting the qualitatively different patterns of brain activity to accompany post-stroke aphasia recovery, a number of physiological factors should be taken into account to choose optimal tDCS parameters. With this in mind, we assess results of ten studies applying tDCS in post-stroke aphasia treatment, and, based on this analysis, suggest directions for further research in this rapidly developing field.