Neural Assimilation and Accommodation in Trilinguals: An fMRI Study at 7 T.

Understanding how multiple languages are represented in the multilingual brain is critical to theories of multilingual assimilation and accommodation. Whether a second language (L2) recruits native-like networks (assimilation) or engages additional neural resources (accommodation) depends partly on the linguistic distance between L1 and L2. However, it remains unclear whether multilinguals can flexibly modulate assimilation and accommodation mechanisms when dealing with different L2 systems. Using 7 T-fMRI, we investigated brain activation patterns during a covert picture-naming task involving one-back phonological retrieval in 15 native Chinese speakers highly proficient in Japanese and English. Whole-brain univariate analysis revealed a common fronto-parieto-occipital network across all three languages (Chinese, Japanese, and English), supporting a shared core language system. However, the Japanese task elicited greater activation in the left lingual and middle occipital gyri, suggesting increased implicit visual-lexical demands. Representational Similarity Analysis (RSA) showed greater pattern similarity between Chinese and English than between Chinese and Japanese, indicating differential neural representation across L2 languages. VOI-based RSA showed a trend toward correlations between Japanese proficiency and representational similarity in the executive regions (pars triangularis and anterior cingulate gyrus), although these correlations did not reach statistical significance. These findings demonstrated that the trilingual brain relied on both assimilation and accommodation, with the level of each modulated by differences in linguistic structure and language experience. Language with a distinct writing system (English) seemed to be assimilated into the dominant L1 Chinese neural framework, whereas orthographically related language (Japanese) rather drove neural accommodation, probably due to script-driven interference. This study highlighted multi-level neural adaptation processes underlying multilingual lexical processing and provided a neurocognitive basis for tailor-made educational strategies considering each student's linguistic background.