Language remains strongly left-lateralized in older adults: A cross-sectional and longitudinal study

Abstract

Language is typically supported by the left hemisphere, but the prevalence and stability of language lateralization in older adults remain unclear. Although acquired language disorders disproportionately affect older adults, most studies of language lateralization have focused on younger populations. We examined language lateralization and its relationship with age in a large cohort of healthy older adults. 115 healthy adults (57 F, 58 M; mean age 59.6 years) completed functional MRI during an adaptive semantic decision task. Lateralization indices were calculated using a bootstrap-based laterality index (LI) approach for whole-hemisphere, frontal, and temporal regions. Relationships between age and lateralization were examined using Pearsons and Bayesian correlation analyses. Fifteen participants completed repeat imaging after a mean interval of 44.2 months. Language activation was strongly left-lateralized, with 96% of participants classified as left-lateralized and 3% as right-lateralized. Frontal and temporal LIs were strongly correlated. No significant relationship was observed between age and lateralization, and no significant longitudinal changes in lateralization were observed. Bayesian analyses supported absence of both age-related effects and longitudinal change in lateralization. Language lateralization remains strongly left-lateralized and unchanging in healthy aging. Findings suggest that aging should not be a factor in the incidence and severity of aphasia from lateralized pathology.