Is inhibition involved in voluntary language switching? Evidence from transcranial direct current stimulation over the right dorsolateral prefrontal cortex.

How do bilinguals freely switch languages in daily life (i.e., voluntary language switching)? Does this involve inhibition of cross-language interference, or does easier lexical access to specific words directly trigger switches to another language? To reveal the underlying mechanism of voluntary language switching, the current study applied transcranial direct current stimulation (tDCS) over the right dorsolateral prefrontal cortex (rDLPFC), an area associated with inhibitory control, to investigate whether and how inhibitory control is involved in voluntary language switching. Interestingly, during the A-tDCS and C-tDCS sessions, bilinguals showed faster naming latencies in repeat trials compared to switch trials, indicating a switch cost. Moreover, the cathodal stimulation exhibited a larger LPC in switching to L2 compared to switching to L1. In contrast, the S-tDCS (sham) session showed no switch cost, faster switch naming latencies compared to the A-tDCS and C-tDCS sessions, and little differences in LPC between switch and repeat trials. Together, these findings suggest that modulating inhibition-related brain regions interferes with voluntary language switching.