Abstract
In recent years, foreign language learning (FLL) has been proposed as a possible cognitive intervention for older adults. However, the brain network and cognitive functions underlying FLL has remained largely unconfirmed in older adults. In particular, older and younger adults have markedly different cognitive profile—while older adults tend to exhibit decline in most cognitive domains, their semantic memory usually remains intact. As such, older adults may engage the semantic functions to a larger extent than the other cognitive functions traditionally considered the most important (e.g., working memory capacity and phonological awareness). Using anatomical measurements and a cognitive test battery, the present study examined this hypothesis in twenty cognitively normal older adults (58–69 years old), who participated in a two-month Italian learning programme. Results showed that the immediate learning success and long-term retention of Italian vocabularies were most consistently predicted by the anatomical measures of the left pars orbitalis and left caudal middle frontal cortex, which are implicated in semantic and episodic memory functions. Convergent evidence was also found based on the pattern of cognitive associations. Our results are consistent with a prominent role of semantic and episodic memory functions in vocabulary learning in older learners.
Highlights
There has been a recent change in attitude, due in part to a series of pioneering studies on the effect of lifelong bilingualism on brain structures and cognitive functions (Bialystok et al, 2007; Luk et al, 2011; Costa and Sebastián-Gallés, 2014; Olsen et al, 2015) and on the neuroplasticity induced by intensive foreign language learning (FLL) in younger adults (Wong and Perrachione, 2007; Mårtensson et al, 2012; Stein et al, 2012; Zatorre, 2013; Qi et al, 2019)
Using a technique known as surface-based morphometry (SBM; Fischl and Dale, 2000; Winkler et al, 2010; Luders et al, 2012), early acquisition of two languages is found to be associated with larger surface area in the left pars opercularis of the inferior frontal gyrus (IFG) and right superior temporal gyrus (STG), while late acquisition is associated with increased mean curvature in the left STG (Hämäläinen et al, 2018)
In support of the hypothesis that semantic functions are important for older language learners, the left pars orbitalis, which is central to semantic control (Sabb et al, 2007; Binder et al, 2009; Ralph et al, 2017) by virtue of its white matter pathway to the semantic hub in the temporal pole (Harvey et al, 2013), was found to be associated with the performance in the in-class quiz and the final test
Summary
In foreign language learning (FLL) research, older adults have been an understudied population (Mackey and Sachs, 2012), which may be caused by the increased difficulty in picking up a new language after the “critical period” (Lenneberg, 1967; Hartshorne et al, 2018, see Wang, 2018). There has been a recent change in attitude, due in part to a series of pioneering studies on the effect of lifelong bilingualism on brain structures and cognitive functions (Bialystok et al, 2007; Luk et al, 2011; Costa and Sebastián-Gallés, 2014; Olsen et al, 2015) and on the neuroplasticity induced by intensive FLL in younger adults (Wong and Perrachione, 2007; Mårtensson et al, 2012; Stein et al, 2012; Zatorre, 2013; Qi et al, 2019). An expansion of the thalamus was observed for individuals with greater immersion in the second language (Pliatsikas et al, 2017; Deluca et al, 2019a)
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