Effects of transcranial direct current stimulation on naming and cortical excitability in stroke patients with aphasia

This study aimed to investigate the effects of anodal transcranial direct current stimulation (A-tDCS) over the left posterior perisylvian region (PPR) on picture naming and cortical excitability measured with electroencephalography (EEG) nonlinear dynamics analysis (NDA) in aphasic patients. Twelve aphasic patients received 20 sessions of speech-language therapy during each of three phases: sham tDCS (Phase A1); A-tDCS to the left PPR (Phase B); and sham tDCS (Phase A2). Picture naming and auditory word-picture identification were measured before and after each phase. The EEG nonlinear index of approximate entropy (ApEn) was calculated for all subjects and 12 normal controls. Picture naming and auditory word-picture identification was significantly improved after phase B. The EEG ApEn analysis indicated that improved picture naming correlated with a higher activation level in wide areas of the left hemisphere and in isolated areas of the right hemisphere after phase B. These results revealed that A-tDCS over the left PPR coupled with speech-language therapy can improve picture naming and auditory comprehension in aphasic patients. tDCS not only modulates activity in the brain region directly underlying the stimulating electrode but also in a network of brain regions that are function-related.