Prefrontal sensitivity to changes in language form and semantic content during speech production.

In bilingual speakers, language switching might involve a change in language form, meaning, or both. However, the neural substrates of language control in the three switching conditions have not been specified. We examined bilingual speech production using a picture-naming paradigm that teased apart language and semantic switching. Bilingual participants named two serially presented pictures, which show the same or different object, with one or two languages. The three switching conditions showed distinct neural activation patterns within the prefrontal cortex. Moreover, neural substrates shared by all switching conditions were primarily found in fronto-parietal regions. Besides, forward switching (L1-to-L2) activated a more widespread neural network than backward switching (L2-to-L1). We discuss differential engagement of the cognitive control system as a function of switching type during bilingual speech production.