Language Experience Impacts Fractal Dimensionality in the Bilingual Brain: a Multivariate Approach

fMRI, Aging, White Matter Integrity

2022-2023

Carleton University, Canada

Bilingualism is reportedly associated with neuroanatomical and cognitive changes. The present
study investigates how bilingualism covaries with the complexity of gray (derived from the
cortical surface volume) and white matter (derived from fibre orientation distributions) topology.
To estimate topological complexity, we computed fractal dimensionality (FD), which is a more
sensitive measure of brain complexity compared to current techniques in capturing GM (e.g.,
cortical thickness and gyrification index) and WM (e.g., diffusion tensor imaging and fractional
anisotropy). Using multivariate partial-least-squares and multiple factor analysis, we examined
how FD covaried with continuous measures of bilingualism derived from a standardized
bilingualism questionnaire (LSBQ) across GM and WM in bilinguals. Results showed that
bilingualism was associated with increased GM cortical complexity, particularly in the left
hemisphere, and reductions in the right hemisphere. Conversely, bilingualism was associated
with decreased WM integrity, especially in the left fornix, the superior longitudinal fasciculus,
and the middle cerebellar peduncle. These findings highlight FD as a valuable method for
capturing neuroanatomical changes in GM and WM as a function of individual differences in
lifelong language experience.