Bilingualism and Structural Network Organization in Temporal Lobe Epilepsy

Abstract

Background and Objectives:There is growing evidence that bilingualism can induce neuroplasticity and modulate neural efficiency, resulting in greater resistance to neurological disease. However, whether bilingualism is beneficial to neural health in the presence of epilepsy is unknown. We tested whether bilingual individuals with temporal lobe epilepsy (TLE) have improved whole-brain structural white matter network organization.Methods:Healthy controls and individuals with TLE recruited from two specialized epilepsy centers completed diffusion-weighted MRI and neuropsychological testing as part of an observational cohort study. Whole-brain connectomes were generated via diffusion tractography and analyzed using graph theory. Global analyses compared network integration (path length) and specialization (transitivity) in TLE versus controls and in a 2 (left vs right TLE) x 2 (bilingual vs monolingual) model. Local analyses compared mean local efficiency of predefined frontal-executive and language (i.e., perisylvian) subnetworks. Exploratory correlations examined associations between network organization and neuropsychological performance.Results:A total of 29 bilingual and 88 monolingual individuals with TLE matched on several demographic and clinical variables, as well as 81 age-matched healthy controls were included. Globally, a significant interaction between language status and side of seizure onset revealed higher network organization in bilinguals compared to monolinguals, but only in left TLE (LTLE). Locally, bilinguals with LTLE showed higher efficiency in frontal-executive, but not in perisylvian networks compared to LTLE monolinguals. Improved whole-brain network organization was associated with better executive function performance in bilingual but not monolingual LTLE.Discussion:Higher structural network organization in bilingual individuals with LTLE suggests a neuromodulatory effect of bilingualism on whole-brain connectivity in epilepsy, providing evidence for neural reserve. This may reflect attenuation of or compensation for epilepsy-related dysfunction of the left hemisphere, potentially driven by increased efficiency of frontal-executive networks that mediate dual-language control. This highlights a potential role of bilingualism as a protective factor in epilepsy, motivating further research across neurological disorders to define mechanisms and develop interventions.

Enhanced efficiency in the bilingual brain through the inter-hemispheric cortico-cerebellar pathway in early second language acquisition

“…Bilingualism provides an optimal model for discerning differences in how the brain wires when a skill is acquired from birth, when the brain circuitry for language is being constructed, and later in life, when the pathways subserving the first language are already well developed. Acquisition of a second language (L2) may have a positive impact on working memory (Kousaie et al, 2021; Kwon et al, 2021), cognitive control (Kousaie et al, 2017), facilitate perception of speech in noise (Kousiae et al, 2019), improve attention (Vega-Mendoza et al, 2015), may bolster cognition in aging (Bialystok et al, 2014), or even imply better prognosis after a brain injury (Alladi et al, 2015) or provide a potential protective benefit in epilepsy (Stasenko et al, 2023). Although, this impact on behavior is influenced by factors such as chronological age or type of task (Gunnerud et al, 2020; Ware et al, 2020), or learning environment (Gullifer et al, 2018), there is significant evidence that bilingualism shapes the brain at the functional (Berken et al, 2016a; Dash et al, 2022) and structural level (Luk et al, 2011; Klein et al, 2014; García-Pentón et al, 2014; Fedeli et al, 2021), and that these effects although most obvious when language is acquired in childhood, can even be observed when languages are learned later in life, and even over relatively short periods of time such as weeks (Barbeau et al 2017).…”

Bilingualism, Epilepsy, and Connectome Resilience

“…In this issue of Neurology ®, Stasenko et al 5 tackled this topic by drawing from a rich literature on the neuroprotective potential of bilingualism in neurologic disease. This retrospective investigation evaluated effects of bilingualism on cortical network organization, studying a multisite cohort of patients with TLE stratified according to disease laterality and bilingual status (left: n = 58, 15 bilinguals/right: n = 59, 14 bilinguals).…”