Seydell-Greenwald, A. | Search bioRxiv

bioRxiv2026

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

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.

neuroscience↗

bioRxiv2020

Spoken language comprehension activates the primary visual cortex

Primary visual cortex (V1) is generally thought of as a low-level sensory area that primarily processes basic visual features. However, in congenitally blind individuals, V1 is involved in language processing, with no evidence of major changes in anatomical connectivity that could explain this seemingly drastic functional change. This is at odds with current accounts of neural plasticity, which emphasize the role of connectivity and conserved function in determining a neural tissues role even after atypical early experiences. To reconcile what appears to be unprecedented functional reorganization with known accounts of plasticity limitations, we tested whether V1 also responds to spoken language in sighted individuals. Using fMRI, we found that V1 in normally sighted individuals was indeed activated by comprehensible speech as compared to a reversed speech control condition, in a left-lateralized and focal manner. Activation in V1 for language was also significant and comparable for abstract and concrete words, suggesting it was not driven by visual imagery. Last, this activation did not stem from increased attention to the auditory onset of words, excluding general attention accounts. Together these findings suggest that V1 responds to verbal information even in sighted individuals, potentially to predict visual input. This capability might be the basis for the strong V1 language activation observed in people born blind, re-affirming the notion that plasticity is guided by pre-existing connectivity and abilities in the typically developed brain. Significance statementHow flexible is the human brain? Studies of congenitally blind individuals showed that language activates the primary visual cortex. This has been interpreted as evidence for unprecedented functional plasticity from a low-level visual to a language area. To reconcile these findings with known limitations of plasticity based on intrinsic physiology and connectivity, we tested if similar activation can be found in sighted participants. We show that left-lateralized primary visual cortex is activated by spoken language comprehension in sighted individuals, . This suggests that plasticity even in complete blindness from birth is not limitless and is guided by pre-existing connectivity and abilities in the typically-developed brain.

neuroscience↗