Effects Of Transcranial Direct Current Stimulation On Language Control

Language control was the ability that inhibition one language and product another during bilingual production processing.Currently,there is increasing attention on how to enhance the ability of language control.Previous studies have demonstrated that the right dorsolateral prefrontal cortex(rDLPFC)plays an important role in inhibiting unrelated stimuli.And transcranial direct current stimulation(tDCS),a noninvasive and safe cortical stimulation technique,which can modulate the excitability of rDLPFC by adjusting the polarity of a current flow,and thereby exchanging the electrical pattern of rest state of brain and improving the performance of cognitive processing.The current study applied transcranial direct current stimulation(tDCS)during the rest state and the task state of language switching to determine whether modulation of rDLPFC would affect language control mechanisms of language switching and the momentary potential distribution maps.In experiment 1,22 unbalance bilinguals undergone three types of stimulation: cathodal stimulation,anodal stimulation and sham stimulation.After each stimulus,64-channel EEG recorded during no-task resting were processed as sequences of momentary potential distribution maps.The sequences were parsed into segments of quasi-stable potential distribution,the “microstates”.The result of microstate showed that higher duration and coverage of class D under the condition of Cathodal stimulus.Compare with Anodal and Sham,the topography of microstate D was shifted by the stimulus of Cathodal,too.Further analysis found that,the shift of microstate D result in DLPFC and cingulate cortex(ACC)decreased the activation by the Cathodal stimulus.Class D was the attention network in the frontal and parietal areas,which were correlated with the interoceptive-autonomic processing.The duration and coverage of microstate D were increasing indicated that the capability of interoceptive-autonomic,such as conflict detection,may be enhanced.ACC and DLPFC was the brain hub of rest state brain network and task-state brain network of general inhibition control.Previous studies showed that the hub was more activity during rest state the less function during task.ACC plays a general role in task monitoring and conflict detection and DLPFC play an important role of inhibited the interference of nontarget.In the current study,the less activity of ACC and DLPFC during rest state indicated that the more easily and efficiency activity during task processing in Cathodal stimulus and the bilingual's ability of conflict detection and inhibited the interference of nontarget may be improved during language switch processing.In the experiment 2,we explored that whether modulation of rDLPFC would affect language control mechanisms by tDCS during language switching.24 unbalance bilinguals have undergone three types of stimulations,too.After each stimulation,participant's behavioral and EEG performed was recorded in picture naming task for language switching.Unbalanced bilinguals exhibited a larger late positive component(LPC)in switching to the weaker language than to the dominant one and similar L1 and L2 switch costs only in the Cathodal tDCS(C-tDCS)session.Further analyses showed that the differences of switch costs(L1 switch costs – L2 switch costs)in the C-tDCS session were smaller than in the Sham-tDCS(S-tDCS)session.Results were largely consistent with the assumption that cathodal stimulation improving inhibitory control abilities of unbalanced bilinguals to help them better inhibit interference.Another possibility is that cathodal stimulation also worked in other brain areas(e.g.,supple-mentary motor area),which potentially altered unbalanced bilinguals' speech planning or abilities to encode task sets.Taking together,tDCS over the rDLPFC shifted the shape of microstate during the rest state and enhanced the ability of language control during task state of language switch processing.The more accurate diverse,such as TMS,should be used for Future studies to proof the relationship of rDLPFC and language control...