Abstract
Bilingualism requires control of multiple language systems, and may lead to architectural differences in language networks obtained from clinical fMRI tasks. Emerging connectivity metrics such as k-core may capture these differences, highlighting crucial network components based on resiliency. We investigated the influence of bilingualism on clinical fMRI language tasks and characterized bilingual networks using connectivity metrics to provide a patient care benchmark. Sixteen right-handed subjects (mean age 42-years; nine males) without neurological history were included: eight native English-speaking monolinguals and eight native Spanish-speaking (L1) bilinguals with acquired English (L2). All subjects underwent fMRI with gold-standard clinical language tasks. Starting from active clusters on fMRI, we inferred the persistent functional network across subjects and ran centrality measures to characterize differences. Our results demonstrated a persistent network “core” consisting of Broca’s area, the pre-supplementary motor area, and the premotor area. K-core analysis showed that Wernicke’s area was engaged by the “core” with weaker connection in L2 than L1.
Highlights
We named the persistent functional architecture across subjects in a particular group at the functional region of interest (fROI)-level the “common network”. This common architecture was constructed for each group by retaining only those pairs of fROIs and those functional links connecting them that were present across all subjects, and we considered the number of appearances of the functional link within the group as a measure of frequency
Both hemispheres demonstrated activation; left hemisphere dominance is clearly observed, which is expected in an fMRI language task among right-handed subjects, as language brain activation is mostly concentrated in the left hemisphere in right-handed individuals[33]
Language skills were evaluated through the Language Experience and Proficiency Questionnaire (LEAP-Q) and proficiency questionnaires, a formal and more extensive neuropsychological evaluation could provide further information regarding subject performance. This should be taken into account in future studies. Both monolingual and bilingual subjects share a common language network formed by BA, preMA, and pre-supplementary motor area (pre-SMA) that occupies the kmax shell and shows features of a central core for language across groups, consistent with our previous results on healthy subjects[15]
Summary
This research aims for the latter, and is based on our group’s recently published work in graph theory and k-core percolation. The goal of this study was to identify the hierarchal relationship of language areas identified by fMRI in monolingual and bilingual subjects with the eventual goal of applying these results to the brain tumor neurosurgical setting
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