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Abstract
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.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
In the last few years, non-invasive brain stimulation methods have been provided useful as adjuvant techniques for language recovery.
The neurophysiological changes induced by transcranial direct current stimulation (tDCS) over the stimulated area and its spatial resolution have not yet been clarified.
In the present study, polarity-dependent tDCS-induced effects were investigated before and after anodic tDCS over the right inferior frontal gyrus (IFG) with simultaneous melodic intonation therapy (MIT) training for the recovery of articulatory disturbances in six aphasic participants.
Neural changes in excitability over the right targeted area were indexed by TMS-evoked potentials (TEPs) and EEG frequency.
Results showed that after the training, there was a greater improvement in response accuracy in speech articulation in the anodic compared to the sham condition, which generalized to untrained items.
Consistent with the behavioral data, the TMS-EEG analysis performed before and after the language treatment showed a modulation of cortical reactivity recorded from the electrodes close to the IFG, regardless of the tDCS condition.
However, the cortical excitability changes were maximized when the MIT treatment was associated with an effective anodal stimulation of the IFG.
Thus, the TMS-EEG data suggest that the anodal stimulation could further increase the beneficial effects of the MIT treatment.
The results fit well with previous data suggesting that potentially adding tDCS to any behavioral therapy may augment the beneficial effects of the stimulation.
Tailored interventions combining tDCS with other brain imaging and neurophysiologic mapping methods in larger samples of subjects may be the most promising innovative approach to aphasia therapy.