Bilateral Transcranial Direct Current Stimulation Language Treatment Enhances Functional Connectivity in the Left Hemisphere: Preliminary Data from Aphasia

Abstract

Several studies have already shown that transcranial direct current stimulation (tDCS) is a useful tool for enhancing recovery in aphasia. However, no reports to date have investigated functional connectivity changes on cortical activity because of tDCS language treatment. Here, nine aphasic persons with articulatory disorders underwent an intensive language therapy in two different conditions: bilateral anodic stimulation over the left Broca's area and cathodic contralesional stimulation over the right homologue of Broca's area and a sham condition. The language treatment lasted 3 weeks (Monday to Friday, 15 sessions). In all patients, language measures were collected before (T0) and at the end of treatment (T15). Before and after each treatment condition (real vs. sham), each participant underwent a resting-state fMRI study. Results showed that, after real stimulation, patients exhibited the greatest recovery not only in terms of better accuracy in articulating the treated stimuli but also for untreated items on different tasks of the language test. Moreover, although after the sham condition connectivity changes were confined to the right brain hemisphere, real stimulation yielded to stronger functional connectivity increase in the left hemisphere. In conclusion, our data provide converging evidence from behavioral and functional imaging data that bilateral tDCS determines functional connectivity changes within the lesioned hemisphere, enhancing the language recovery process in stroke patients.

Brain connectivity and neurological disorders after stroke

“…The treatment induced significant behavioral amelioration of motor functions as well as increased functional connectivity of ipsilesional motor cortex with contralateral premotor cortex and bilateral precuneus. Similarly, in the language domain, Marangolo et al [39] investigated the effects of tDCS on language recovery and resting state functional connectivity in a small group ( n = 9) of aphasic patients with articulatory deficits. Patients underwent two 15-day sessions of language therapy and real or sham tDCS treatment with a 14-day intersession interval between the real and the sham condition.…”

Adaptive Plasticity in the Healthy Language Network: Implications for Language Recovery after Stroke

“…In this context, the systematic application of different NIBS protocols over various temporal regions should also be addressed. This should include the comparison of unifocal TMS effects with dual-site stimulation ([150], see above) and the systematic investigation of bilateral tDCS effects, for example, with the anode placed over a left-hemispheric language region and the cathode over the right-hemispheric homologue [166]. Other studies suggest that modelling the current flow on an individual basis might help to optimize NIBS effects at the target region and might thus be used to increase therapeutic efficiency in future studies [167].…”

Transcranial direct current stimulation effects on neural processing in post‐stroke aphasia

“…This is likely explained by the limited understanding of how tDCS modulates brain functions in stroke patients and whether stimulation effects of specific montages overlapped with the neural networks engaged during treatment. Indeed, while a number of studies have demonstrated that tDCS can enhance treatment‐induced motor recovery and neural plasticity in stroke patients [Allman et al, ; Lefebvre et al, ; Lindenberg et al, ; Stagg et al, ], only one study investigated the underlying mechanisms of superior treatment effects due to tDCS in aphasia [Marangolo et al, ]. In this study, the combination of language therapy and bi‐frontal tDCS resulted in enhanced connectivity within the lesioned left hemisphere compared with treatment and sham‐tDCS.…”

“…This task was chosen as naming impairment is among the most common symptoms of aphasia [Lazar and Antoniello, ] which has frequently been targeted in previous tDCS trials in aphasia (for review see De Aguiar et al []). To assure that potential changes in neural processing due to tDCS were not confounded by performance [Fridriksson and Morrow, ; Price et al, ] or treatment effects [Lefebvre et al, ; Lindenberg et al, ; Marangolo et al, ; Stagg et al, ], we only included object pictures that could be named correctly by individual patients during repeated baseline assessments. Intrascanner tDCS targeted the left primary motor cortex (M1), a montage that improved short‐ and long‐term naming treatment outcome and everyday communication compared with treatment with sham‐tDCS in a previous clinical trial of our group [Meinzer et al, ].…”