A Singaporean study by X. Li et al titled “Brain gray matter morphometry relates to onset age of bilingualism and theory of mind in young and older adults” published on 8 February 2024 confirms what is generally known or at least suspected: that bilinguals have better brains, even as they age.
The paper is 13 pages long. The main text is about 9 pages, the remaining are mostly references. I think the paper can describe more of the specifics regarding the tests and present the results better but it is generally interesting nonetheless.
The study involved two groups: 46 young adults with a mean age of 21.87 years (ranging from 19 to 30 years), and 50 older adults with a mean age of 63.56 years (ranging from 54 to 77 years). Overall, there were 66 females and 30 males. Amongst other conditions, participants must have “no history of neurological or psychiatric illnesses”.
All spoke English and Mandarin as two of their languages, with most having knowledge of a third or even fourth language. Both groups used their two most-used languages around 95% of the time in a typical week. Although the “young adults acquired their second language at ages significantly earlier than the older adults”, most participants’ second language age of acquisition (L2AoA) was between ages 1 to 6 years. It should be noted that L2AoA is the initial exposure.
Participants carried out Theory of Mind (ToM) assessments that involved questions and tasks as well as an MRI scan.
In short, the study found
…that earlier age of bilingual acquisition and better ToM performance were associated with larger gray matter volume, higher cortical thickness, and larger surface area in distributed brain regions implicated in functions related to mental state representation, language processing, and cognitive control. This morphometric pattern associated with ToM was stronger in the older participants than younger participants, but its association with L2AoA was comparable across both age groups. An important finding of this study is the significant association between age of second language onset and bilinguals’ brain structure, which was also related to their ToM abilities. In support of our main hypothesis, we showed that more brain reserve, as measured by gray matter metric, was associated with earlier L2AoA and better ToM performance in young and older adults. Our results provide novel evidence for how early onset age of bilingualism may modulate the developmental course of ToM abilities across the adulthood, going beyond the focus of previous work in cognitive aging on general cognitive abilities.
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