Cathodal transcranial direct current stimulation over right dorsolateral prefrontal cortex improves language control during language switching.

Currently, there is increasing attention on how to best improve language control efficiency and minimize cross-language interference in bilinguals. Previous studies have demonstrated that right dorsolateral prefrontal cortex (rDLPFC) plays an important role in inhibiting unrelated stimuli. The current study applied transcranial direct current stimulation (tDCS) during language switching to determine whether modulation of rDLPFC would affect language control mechanisms. All the participants have undergone three types of stimulations: cathodal stimulation, anodal stimulation and sham stimulation. The sequence of three stimulations was counterbalanced across participants. After each stimulation, participants performed 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., supplementary motor area), which potentially altered unbalanced bilinguals' speech planning or abilities to encode task sets.