Theta burst stimulation of dorsolateral prefrontal cortex modulates pathological language switching: A case report

Although different lesion and neuroimaging studies had highlighted the importance of the dorsolateral prefrontal cortex (DLPFC) in language switching, the nature of this higher cortical disorder of communication and its neural correlates have not been clearly established. To further investigate the functional involvement of the DLPFC, we used transcranial magnetic stimulation (TMS) given as theta burst stimulation (TBS) in a bilingual patient showing pathologic language switching after an ischemic stroke involving the left frontal lobe. Inhibitory and excitatory TBS were applied to the left DLPFC, to the right DLPFC, or to an occipital cortical control site. A short-lasting interruption of the pathological language switching occurred after excitatory left DLPFC stimulation, while inhibitory left DLPFC TBS transiently increased the number of utterances produced in the unwanted second language. Effects were non-significant after right DLPFC and occipital TBS. Our findings suggest that left DLPFC is actively involved in language switching. TMS techniques may help in understanding the neural bases of bilingualism.