When Age Tips the Balance: a Dual Mechanism Affecting Hemispheric Specialization for Language

Abstract

Aging engenders neuroadaptations, generally reducing specificity and selectivity in functional brain responses. Our investigation delves into the functional specialization of brain hemispheres within language-related networks across adulthood. In a cohort of 728 healthy adults spanning ages 18 to 88, we modeled the trajectories of inter-hemispheric asymmetry concerning the principal functional gradient across 37 homotopic regions of interest (hROIs) of an extensive language network, known as the Language-and-Memory Network. Our findings reveal that over two-thirds of Language-and-Memory Network hROIs undergo asymmetry changes with age, falling into two main clusters. The first cluster evolves from left-sided specialization to right-sided tendencies, while the second cluster transitions from right-sided asymmetry to left-hemisphere dominance. These reversed asymmetry shifts manifest around midlife, occurring after age 50, and are associated with poorer language production performance. Our results provide valuable insights into the influence of functional brain asymmetries on language proficiency and present a dynamic perspective on brain plasticity during the typical aging process.

Dynamics of White Matter Architecture in Lexical Production among Middle-Aged Adults

“…Temporally, the WM networks most affected by age (i.e., Net 16, 5, 11, 4) showed the largest microstructural alterations occurring from age 53 onwards. This aligns with previous studies concluding that discontinuities (i.e., nonlinear trajectory) in brain structure are likely to onset at middle age (Beck et al, 2021; Park & Festini, 2016) and further reinforces the idea that midlife is a critical period of major brain structural reorganization in line with reports on brain function and language performance (Deery et al, 2023; Hennessee et al, 2022; Park & Festini, 2016; Roger et al, 2023; Shafto & Tyler, 2014). Overall, our study supports the current evidence that dorso-ventral association (SLF II/III, MLF) and anterior cortico-subcortical pathways suffer the largest age-related microstructural alterations (Gunning-Dixon et al, 2009; Park & Festini, 2016; Yeatman et al, 2014).…”

Atlas for the Lateralized Visuospatial Attention Networks (ALANs): Insights from fMRI and Network Analyses

“…Similarly, the inferior frontal sulcus (f2_2), a hub for the ParietoFrontal network, was also a central region in the core network of SENSAAS and is on the verge of being a hub (Labache et al, 2019). Furthermore, recent findings reveal that with aging, language processing regions in the left hemisphere shift from leftward asymmetry to bilateral organization, similarly affecting the mnemonic regions’ symmetry (Roger et al, 2023). This reorganization suggests a nuanced interplay between language, memory, and visuospatial attention over time.…”

Lifespan Oscillatory Dynamics in Lexical Production: A Population-based MEG Resting-State Analysis

“…Given the nonlinear age trajectory reported in MEG studies 62 , we generated two piecewise polynomials that we included as separate variables in our models. The quadratic term used to generate the polynomials was centered at 55 years old based on converging evidence in different imaging modalities 19,66,67,113 and matched to the original scale of the age variable.…”