Bilingualism at the core of the brain. Structural differences between bilinguals and monolinguals revealed by subcortical shape analysis

Abstract

Naturally acquiring a language shapes the human brain through a long-lasting learning and practice process. This is supported by previous studies showing that managing more than one language from early childhood has an impact on brain structure and function.However, to what extent bilingual individuals present neuroanatomical peculiarities at the subcortical level with respect to monolinguals is yet not well understood, despite the key role of subcortical gray matter for a number of language functions, including monitoring of speech production and language control -two processes especially solicited by bilinguals. Here we addressed this issue by performing a subcortical surfacebased analysis in a sample of monolinguals and simultaneous bilinguals (N=88) that only differed in their language experience from birth. This analysis allowed us to study with great anatomical precision the potential differences in morphology of key subcortical structures, namely, the caudate, accumbens, putamen, globus pallidus and thalamus.Vertexwise analyses revealed significantly expanded subcortical structures for bilinguals compared to monolinguals, localized in bilateral putamen and thalamus, as well as in the left globus pallidus and right caudate nucleus. A topographical interpretation of our results suggests that a more complex phonological system in bilinguals may lead to a greater development of a subcortical brain network involved in monitoring articulatory processes.

Immersive bilingualism reshapes the core of the brain

“…Following that, subcortical structures were segmented with FIRST (Patenaude et al 2011), an analysis tool implemented in FSL. Based on the effects reported in Burgaleta et al (2016), we automatically segmented the thalamus, globus pallidus, putamen, and the caudate nucleus. Quality control of the segmented images was performed by an experienced researcher.…”

“…Burgaleta et al (2016) suggested that this is because of the preferred method of use in the majority of these studies, i.e., VBM, which may not be optimal in accounting for the shape and size of subcortical structures (Zatorre et al 2012). To overcome this, Burgaleta and colleagues used the shape analysis technique FIRST (Patenaude et al 2011) which can account better for regional variations in the shape of subcortical structures.…”

“…Based on that finding, this study investigated whether immersive bilingualism also has an effect on the shape of subcortical structures. Using the protocol presented in Burgaleta et al (2016), we compared the subcortical structure of two groups of sequential bilinguals with different amounts of L2 immersion, against monolingual controls: (a) the groups from Pliatsikas et al (2015), including bilingual participants of high linguistic immersion in the UK, and (b) the groups from Pliatsikas et al (2014a, b), including bilinguals of comparable L2 proficiency and AoA but with limited L2 immersion. If the previously reported subcortical effects are due to continuous usage of two languages, rather than their simultaneous acquisition, we would expect them to be replicated in our group of highly immersed sequential bilinguals too, but not in the group with limited immersion.…”

Beyond Bilingualism: multilingual experience correlates with caudate volume

“…in individuals who speak 3 languages or more, would be systematically and positively related to the volumes of these two subcortical structures. It is worth noting that two previous studies (Burgaleta et al, 2016;Pliatsikas, DeLuca, Moschopoulou, & Saddy, 2016) have found that the caudate nuclei of bilinguals are relatively larger compared to those of monolinguals.…”

“…The caudate nuclei have been shown to play a role in both language control (Crinion et al, 2006;Hervais-Adelman et al, 2015) and cognitive control (Grahn, Parkinson, & Owen, 2008), and have previously been shown to be enlarged in bilinguals vs. monolinguals (Burgaleta et al, 2016;Pliatsikas, DeLuca, Moschopoulou, & Saddy, 2016). Although there is also evidence for a role of the putamen in multilingual control, it may be that the absence of an observed relationship between putaminal structure and LEXP is due to the nature of its role: if, as suggested by Hervais-Adelman and colleagues (2015), the caudate is implicated in managing lexico-semantic sets as a function of task demands (c.f.…”