Sequence of language acquisition as a factor determining language comprehension centre location in cerebral cortex in sequential multilinguals.

Aim of study: The objective of this study was to identify cerebral regions specifically involved in speech comprehension for each sequentially acquired language (L1, L2, L3, L4) in multilingual individuals, and to explore the relationship between the sequence of language acquisition and its cortical representation.

Clinical rationale for study: Multilingualism is increasingly prevalent worldwide. However, the cortical representation of sequentially acquired languages remains inadequately explored. Currently, there are no established guidelines for the perioperative neurosurgical management of multilingual patients, presumably due to a lack of research on this topic.

Material and methods: Participants with a high communicative proficiency in at least three sequentially acquired foreign languages, learned after the age of three, were recruited. A passive listening paradigm was applied for this study. Brain anatomy was visualized using T1-weighted MRI, while functional brain activity (BOLD signal) was measured using echo-planar imaging. Cortical activity elicited by foreign languages (L2, L3, L4) was compared with native language (L1) and an 'unknown' (LN). Data processing and statistical analysis were conducted using SPM12 software.

Results: Twenty multilingual participants were included. A gradual decrease in left-hemisphere dominance was observed from L1 through L4. Compared to L1, L2 demonstrated increased cortical activation in the right middle temporal gyrus and left middle occipital gyrus, whereas L3 showed higher activation in the left fusiform gyrus. No areas of greater activation were identified for L4 compared to L1. Conversely, L1 showed numerous regions of heightened activation relative to subsequently acquired languages. When compared to LN, both L2 and L3 exhibited increased activity in the right insula. Additionally, L3 and L4 displayed elevated activity in the right hippocampus compared to LN.

Conclusions and clinical implications: Our study found distinct cortical localizations for sequentially acquired languages. We recommend routine perioperative cortical mapping for languages L2 and L3, in addition to L1. Mapping for L4 should be considered on a case-by-case basis. Further research into cortical areas involved in multilingual speech production is warranted.