Evidence of a large-scale network underlying language switching: a brain stimulation study.

This 47-year-old, right-handed bilingual (French and English) man underwent awake surgery for a glioma in the left dominant posterior temporal lobe. During intraoperative picture naming, direct electrostimulation of a discrete cortical area within the posterior part of the superior temporal sulcus elicited an involuntary language switching (French to English). Moreover, during tumor resection, subcortical electrical mapping again generated reproducible language switching (French to English) when stimulating the superior longitudinal fasciculus. After transient immediately postoperative worsening, the patient recovered normal language performance. Both 7 days and 2 months later, however, another language switching episode (French to English) was observed during a naming task. Thus, both intraoperative mapping and transient postsurgical disturbances support involvement of the left dominant posterior temporal area and the superior longitudinal fasciculus in language switching. Interestingly, this pathway is known to connect the posterosuperior temporal gyrus to the Broca center, a region the authors have described as inducing possible switching on stimulation. Therefore, the authors suggest the existence of a large-scale distributed network subserving language switching. Such knowledge may have important clinical implications for the surgical care of a bilingual patient harboring a lesion in the left hemisphere.