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.
Recent studies have shown that action observation treatment without concomitant verbal cue has a positive impact on the recovery of verb retrieval deficits in aphasic patients. In agreement with an embodied cognition viewpoint, a hypothesis has been advanced that gestures and language form a single communication system and words whose retrieval is facilitated by gestures are semantically represented through sensory-motor features. However, it is still an open question as to what extent this treatment approach works. Results from the recovery of motor deficits have suggested that action observation promotes motor recovery only for actions that are part of the motor repertoire of the observer. The aim of the present experiment was to further investigate the role of action observation treatment in verb recovery. In particular, we contrasted the effects induced by observing human actions (e.g. dancing, kicking, pointing, eating) versus non human actions (e.g. barking, printing). Seven chronic aphasic patients with a selective deficit in verb retrieval underwent an intensive rehabilitation training that included five daily sessions over two consecutive weeks. Each subject was asked to carefully observe 115 video-clips of actions, one at a time and, after observing them, they had to produce the corresponding verb. Two groups of actions were randomly presented: humans versus nonhuman actions. In all patients, significant improvement in verb retrieval was found only by observing video-clips of human actions. Moreover, follow-up testing revealed long-term verb recovery that was still present two months after the two treatments had ended. In support of the multimodal concept representation's proposal, we suggest that just the observation of actions pertaining to the human motor repertoire is an effective rehabilitation approach for verb recovery.
Despite the fact that different studies have been performed using transcranial direct current stimulation (tDCS) in aphasia, so far, to what extent the stimulation of a cerebral region may affect the activity of anatomically connected regions remains unclear. The authors used a combination of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) to explore brain areas' excitability modulation before and after active and sham tDCS. Six chronic aphasics underwent 3 weeks of language training coupled with tDCS over the right inferior frontal gyrus. To measure the changes induced by tDCS, TMS-EEG closed to the area stimulated with tDCS were calculated. A significant improvement after tDCS stimulation was found which was accompained by a modification of the EEG over the stimulated region.
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