Lifelong exposure to multilingualism: new evidence to support cognitive reserve hypothesis

Abstract

Objective: Investigate the protective effect of multilingualism on cognition in seniors.

Methods: As part of the MemoVie study conducted on 232 non-demented volunteers aged 65 and more, neurogeriatric and neuropsychological evaluations were performed. Participants were classified as presenting either cognitive impairment without dementia (CIND) or being free of any cognitive impairment (CIND-free). Language practices, socio-demographic data and lifestyle habits were recorded. In this retrospective nested case-control design, we used as proxies of multilingualism: number of languages practiced, age of acquisition and duration of practice, emphasizing the temporal pattern of acquisition, and the resulting practice of several languages sequentially or concomitantly during various periods of life. This special angle on the matter offered to our work a dimension particularly original and innovative.

Results: 44 subjects (19%) had CIND, the others were cognitively normal. All practiced from 2 to 7 languages. When compared with bilinguals, participants who practiced more than 2 languages presented a lower risk of CIND, after adjustment for education and age (odds ratio (OR) = 0.30, 95% confidence limits (95%CL) = [0.10-0.92]). Progressing from 2 to 3 languages, instead of staying bilingual, was associated with a 7-fold protection against CIND (OR = 0.14, 95%CL = [0.04-0.45], p = 0.0010). A one year delay to reach multilingualism (3 languages practiced being the threshold) multiplied the risk of CIND by 1.022 (OR = 1.022, 95%CL = [1.01-1.04], p = 0.0044). Also noteworthy, just as for multilingualism, an impact of cognitively stimulating activities on the occurrence of CIND was found as well (OR = 0.979, 95%CL = [0.961-0.998], p = 0.033).

Conclusion: The study did not show independence of multilingualism and CIND. Rather it seems to show a strong association toward a protection against CIND. Practicing multilingualism from early life on, and/or learning it at a fast pace is even more efficient. This protection might be related to the enhancement of cognitive reserve and brain plasticity, thereby preserving brain functions from alterations during aging.

Figure 1. Acquisition of multilingualism in the studied population.

Part A. Typical progression: sequential and increasing process of learning and practicing multilingualism. (For each stage of multilingualism, either individuals stayed at a specified level, or they progressed to the next step i.e. they learned an additional language.) Description of the 6 models of progression found among the 168 individuals for which the learning process represents the acquisition of one language after another (keeping the practice of all of them). Part B. Atypical and unordered progression of learning and practicing multilingualism. Illustration of the 6 models of atypical progression exhibited by the 64 subjects learning 2 or 3 languages in the same period of time and/or losing the practice of one or 2 languages at some point in their lives.

Figure 2. Association between different stages of multilingualism and CIND.

Forest plot of the OR comparing different stages of multilingualism over lifetime, to bilingualism, trilingualism and/or quadrilingualism. The solid vertical line shows an OR of 1 (no effect). Each multilingual status is represented by a square, the size of which shows the corresponding sample size in the analysis. The symbols represent the four different analysis performed. The lozenge at the top shows the overall effect of speaking “more than two languages” versus “exactly two languages”. The CL for each situation is represented by a horizontal line and the lower and upper control limits are indicated next (LCL, UCL).