Beyond volume: A surface-based approach to bilingualism-induced grey matter changes

Abstract

Bilingualism is a sustained experience associated with structural changes in cortical grey matter (GM) morphology. Apart from a few studies, a dominant method used to assess bilingualism-induced GM changes has been the voxel-based morphometry (VBM) analysis. While VBM is sensitive to GM volume/density differences in general, it cannot be used to identify whether the observed difference is due to relative changes in, e.g., cortical thickness, area or folding, as it uses a single combined measure of them all. Here, we used surface-based analysis (SBA) approach to investigate whether early acquisition of a second language (L2) affects the cortical GM morphology relative to late L2 acquisition. More specifically, our aim was to test a hypothesis that early acquisition of two languages induces GM changes that are predominantly surface area-driven, while late acquisition is supposedly characterised with primarily thickness-driven changes. To this end, several surface-based measures were concurrently compared between the groups. In line with the hypothesis, the results revealed that early bilingual experience is associated with significantly extended cortical surface area over the left pars opercularis and the right superior temporal gyrus. Contrary to our expectations, however, we found no evidence supporting the postulated association between late L2 acquisition and increased cortical thickness. Nevertheless, our study highlights the importance of including cortical surface measures when investigating bilingualism-related GM modulations.

Education modulates brain maintenance in presymptomatic frontotemporal dementia

“…Some evidence shows that cognitive stimulating environments lead to brain volumetric advantages and better cognitive performances. These effects are common to physiological [24][25][26] and initial pathological ageing, [27][28][29] suggesting that neuroplasticity is maintained even in diseased brains, regardless of the specific clinical picture or the underlying pathological process.…”

Understanding structural plasticity in the bilingual brain: The Dynamic Restructuring Model

“…A similar pattern was reported by Grogan, Parker Jones, Ali, Crinion, Orabona, Mechias, Ramsden, Green and Price (2012), who reported greater GM density in the right IPL for sequential multilinguals vs. bilinguals. In a different group of studies, Hämäläinen and colleagues (Hämäläinen, Joutsa, Sihvonen, Leminen & Lehtonen, 2018; Hämäläinen et al, 2017) also showed that acquiring a third language sequentially after two languages have already been acquired leads to increased GM in the left IFG and STG, and increased FA and decreased MD in the IFOF, compared to trilinguals with two sequentially acquired languages. Therefore, it appears that sequential acquisition of a third language or beyond follows a pattern of structural changes similar to those caused by sequential acquisition of a second language, suggesting that previously modulated regions need to re-adapt in order to accommodate the additional language(s).…”

The effect of bilingualism on brain development from early childhood to young adulthood

“…Indeed, the reported structural effects of bilingualism in adults (measured as differences between bilingual and monolingual groups, or sometimes in training studies) are most commonly reported in grey matter regions that have been found to underlie such language-related (as well as other) processes (for details, see Pliatsikas 2019 ). These regions primary include: frontal and nearby cortex, including the three portions of the left inferior frontal gyrus (IFG), namely, opercularis (IFGop), triangularis (IFGtr), and orbitalis (IFGor), as well as the frontal pole, the middle and superior frontal gyri (MFG and SFG), and the anterior cingulate cortex (ACC); temporal cortex, including the superior, middle, and inferior temporal gyri (STG, MTG and ITG), Heschl’s gyrus, the temporal pole, and the hippocampus; and parietal cortex, including the supramarginal gyrus, the angular gyrus, and the superior parietal lobule (Mechelli et al 2004 ; Mårtensson et al 2012 ; Abutalebi et al 2014a ; Klein et al 2014 ; Stein et al 2014 ; Kaiser et al 2015 ; Olulade et al 2016 ; Hämäläinen et al 2018 ). Subcortical structures that are affected mainly include the basal ganglia, in particular the caudate nucleus, the putamen, and the globus pallidus, as well as the thalamus (Burgaleta et al 2016 ; Pliatsikas et al 2017 ; DeLuca et al 2019a ), with some effects also having been reported in the cerebellum (Filippi et al 2011 , 2020 ; Pliatsikas et al 2014 ).…”