An fMRI study of English and Spanish word reading in bilingual adults.

Reading relies on a left-lateralized brain system, including occipito-temporal (OTC), temporo-parietal, and inferior frontal (IFC) cortices. Neuroimaging studies have investigated whether activation in these cortices is modulated by a language's orthographic depth (consistency of grapheme-to-phoneme conversion). In Spanish-English bilinguals, some but not all studies have reported activation differences between the two languages during reading. Here, we studied Spanish-English early bilingual adults living in the United States (N = 25; 17 females, 8 males). We examined local activity, functional connectivity, and spatially distributed activity patterns during English and Spanish word reading. We found overlap in local activity for the two languages in the left IFC, but no differences in activation between them and few differences in functional connectivity (none of which were in pairs of regions known to be involved in reading); yet, there were spatially distributed patterns of brain activity that differentiate English and Spanish in regions of bilateral cerebellum/left OTC, the left superior occipital gyrus, the left IFC, and the left medial frontal gyrus. Overall, we found no evidence for differences in local activation or functional connectivity during English versus Spanish word processing in regions known to be involved in reading, yet we found brain-based evidence that Spanish-English bilinguals distinguish between the two languages.