Bihemispheric tDCS enhances language recovery but does not alter BDNF levels in chronic aphasic patients

Purpose: Several studies have shown that transcranial direct current stimulation (tDCS) is a useful tool to enhance language recovery in aphasia. It has also been suggested that modulation of the neurotrophin brain-derived neurotrophic factor (BDNF) might be part of the mechanisms involved in tDCS effects on synaptic connectivity. However, all language studies have previously investigated the effects using unihemispheric stimulation. The purpose of the present study is to investigate the role of bihemispheric tDCS on language recovery and BDNF serum levels. Methods: Seven aphasic persons underwent an intensive language therapy in two different conditions: real bihemispheric stimulation over the left and right Broca's areas and a sham condition. Results: After the stimulation, patients exibited a significant recovery in three language tasks (picture description, noun and verb naming) compared to the sham condition which persisted in the follow-up session. No significant differences were found in BDNF serum levels after tDCS stimulation and in the follow-up session. However, a significant positive correlation was present for the real stimulation condition between percent changes in BDNF levels and in the verb naming task. Conclusions: The data suggest that this novel approach may potentiate the recovery of language in chronic aphasia. They also emphasize the importance to further investigate the role of possible biomarkers associated with tDCS treatment response in language recovery.