Comparing cortical organization and semantic tuning across bilingual brains

In bilingual individuals, the brain regions involved in processing semantics in native and non-native languages are broadly overlapping and represent largely similar semantic concepts, although fine-grained differences exist. However, how these broad similarities and fine-grained differences vary across individuals remains unclear. Here, we compared the spatial cortical organization and semantic tuning of semantic representations using functional magnetic resonance imaging (fMRI) data from six Chinese-English bilingual participants who read several hours of narratives in both languages. We fit voxelwise encoding models separately for each participant and language and applied hierarchical clustering to group-averaged estimated model weights to derive a common set of semantic clusters. We then compared the cortical organization and semantic tuning of these clusters across participants and languages. For all clusters, cortical overlap was higher across languages within a participant than across participants within a language. Semantic tuning similarity showed the opposite pattern, suggesting largely shared tuning across participants within the same language. Cross-participant semantic tuning similarity was lower for the communication and family clusters than for the other clusters, suggesting greater individual variability for social concepts. Together, these findings reveal a participant-specific spatial cortical organization that is preserved across languages and fine-grained language-specific patterns of semantic tuning largely shared across participants.