Improvement in naming with tDCS and alteration of functional connectivity in post-stroke aphasia: A randomized controlled trial

Background This study aimed to investigate the effects of anodal transcranial direct current stimulation (A-tDCS) over the left Sylvian parietal temporal region (SPT) on picture naming and changes in brain functional connectivity in post-stroke aphasic patients. Methods This is a double-blind, sham-controlled, randomized controlled study. Sixty aphasic patients were randomly assigned to receive either active or sham tDCS over the SPT as well as speech-language therapy for four weeks. Standardized aphasia assessments and electroencephalogram (EEG) examinations were conducted before and after the treatment. The EEG nonlinear index of cross approximate entropy (C-ApEn) was used to assess brain functional connectivity. Results The tDCS group demonstrated significantly greater improvements than the control group in both picture naming and auditory word-picture identification scores ( p  < 0.001). Regression analysis revealed that the group (tDCS/control) was the primary factor associated with improving picture naming. The functional connectivity of F3-P3, F7-P3, T3-T5, T5-P3, T5-C3, C3-P3, T4-T6, T3-T4, and T5-T6 significantly increased following tDCS. Conclusions A-tDCS targeting the left SPT region can improve picture naming in patients with subacute post-stroke aphasia. Both direct and indirect connections within language networks in the left hemisphere were partially elevated, and functional connectivity between the executive control network and the language network was enhanced. Additionally, activation was observed in some connections within the right hemisphere and between the bilateral hemispheres. The analysis of brain functional connectivity provides neural network evidence for the effect of tDCS in enhancing naming abilities in stroke patients with aphasia. Clinical trial registry number: ChiCTR-TRC-14005072