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Recruiting the “right” hemisphere in foreign language learning in ageing brain—Evidence from diffusion-MRI
Poster Session C, Friday, October 25, 4:30 - 6:00 pm, Great Hall 3 and 4
Xavreila Sheung-Wa Ng1, Manson Cheuk-Man Fong1, Matthew King-Hang Ma1, Fangfei Li1, Jiaxin Chen1, Nga-Yan Hui1, Cloris Pui-Hang Li1, William Shiyuan Wang1; 1The Hong Kong Polytechnic University
Introduction. The hemispheric asymmetry reduction in older adults (HAROLD) refers to a less lateralised frontal activity during cognitive performance (Cabeza, 2002), in response to age-related neurocognitive decline. Anatomical evidence for such compensation was observed in our previous study on foreign language learning (FLL; Fong et al., 2022). In the present experiment, we sought to obtain converging evidence on such compensatory processes based on diffusion-weighted imaging and examine the hypothesis that the commissural (specifically corpus callosum, CC) or right-hemispheric association fibres (arcuate fasciculus, AF; uncinate fasciculus, UF) are more strongly associated with FLL performance in older than younger adults. The CC is crucial for its role in interhemispheric communication, and has been shown to grant older adults a performance advantage in tasks that entail both hemispheres (Reuter-Lorenz & Stanczak, 2022). Thus, if FLL similarly recruits both hemispheres, it is plausible that FLL performance is partially mediated by the microstructure of CC. Similarly, as the left AF and UF are major pathways supporting language, under the HAROLD hypothesis, their right-hemispheric counterparts would also be associated with FLL performance. Method. Participants were 47 (older: 12F/12M; younger: 12F/11M) cognitively normal, right-handed, Cantonese-English bilinguals matched in education. Following a three-month Italian learning programme, diffusion data were acquired using a multi-shell sequence (b=1500 and 3000s/mm2; direction=99; voxel size=1.5mm). The data were analysed using DSI studio. Specific focus was placed on number of tracts (NumTract) and fractional anisotropy (FA). The vocabulary and grammar learning performance were evaluated every three lessons and through a final test. Accuracy served as the main performance metric while reaction time (RT) a supporting metric since it is often muddled by processing speed. Result. For CC, in older learners, FA was correlated with vocabulary accuracy (lessons, Spearman’s rho=.42, p=.040; test, rho=.43, p=.035), vocabulary RT (lessons, rho=-.56, p=.004), and grammar accuracy (lessons, rho=.43, p=.037). In younger adults, only association with vocabulary RT was found, and only for NumTract (lessons, rho=-0.51, p=.014). For AF, NumTract was positively correlated with older learners’ vocabulary accuracy for the right hemisphere (RH) (lessons, rho=.65, p=.015). For younger learners, NumTract was positively correlated with their grammar accuracy for LH (test, rho=.48, p=.026). For UF, FA correlated positively with older learners’ vocabulary accuracy for LH (lessons, rho=.49, p=.015), while NumTract correlated with grammar accuracy for RH (lessons, rho=.54, p=.006). Discussion. In older adults, vocabulary acquisition is benefitted by an intact CC, while grammar accuracy is associated with a more bundled right UF. As for AF, although the NumTract is a significant predictor of accuracy for both age-groups for LH, only older adults exhibited a positive correlation with the vocabulary accuracy for RH. One should be cautioned that the AF is thinner on the RH on average, making it prone to unsuccessful reconstruction. Nonetheless, significant association could still be found at this smaller effective sample size. Taken together, our results lend further support to the HAROLD model. As such, the right hemisphere should be incorporated in future neurolinguistic studies on ageing. This research was supported by HKRGC-GRF 15606119.
Topic Areas: Multilingualism,