Biology subjects

Day, T. K. M.

Publications and source records attributed to Day, T. K. M..

4 recordsLinked to original sources

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↗

bioRxiv2025

Identifying left and right hemispheres using functional connectivity

Many studies have analyzed what organizational features distinguish the left and right hemispheres of the human brain, with differences typically being found in language areas and in fine motor control (i.e., handedness). In this analysis, we test whether supervised learning can categorize ("fingerprint") an unseen hemisphere as right or left based on functional connectivity. Using data from the Human Connectome Project, we find success to be extremely high (accuracies > .90) in models trained on right-handed participants (Edinburgh Handedness Inventory [EHI] > 0) and in models trained on left-handed participants (EHI [≤] 0). In a second analysis, we test whether the same can be done to identify handedness alongside hemisphere left/right sidedness. While individuals hemispheres are less distinct the more left-handed they are, hemiconnectomes cannot be reliably classified as belonging to a left- or right-handed person. Our approach can inform developmental and post-injury work on hemispheric organization and reorganization.

neuroscience↗

bioRxiv2025

Commonality and Variability in Functional Networks In Young Children Under 5 Years Old

Functional brain networks support human cognition, yet how individualized network architecture emerges in early childhood remains poorly understood. Averaging across participants can obscure age-specific organization and person-to-person differences, particularly in slowly developing association cortices. We developed an age-appropriate functional reference that captured common structure across toddlers without averaging away individual variability, enabling estimation of each childs networks from resting-state fMRI. Across cohorts of 8-60-month-old children, we found individualized network organization--including finer-scale subdivisions and emerging language lateralization--well before age five. Network layouts showed longitudinal stability, with greater consistency in sensory than association regions. Within-network connectivity was stronger and explained age-related variance when networks were defined using individualized rather than group-consensus topography. Left-lateralization of language networks tracked age-normalized verbal ability, linking early functional architecture to emerging cognition. These findings show that behaviorally relevant brain networks arise far earlier than previously recognized, providing a foundation for studying typical development and early biomarkers.

neuroscience↗

bioRxiv2024

A subset of brain regions within adult functional connectivity networks demonstrate high reliability across early development

The human cerebral cortex contains groups of areas that support sensory, motor, cognitive, and affective functions, often categorized into functional networks. These networks show stronger internal and weaker external functional connectivity (FC), with FC profiles more similar within the same network. Previous studies have shown these networks develop from nascent forms before birth to their mature, adult-like structures in childhood. However, these analyses often rely on adult functional network definitions. This study assesses the potential misidentification of infant functional networks when using adult models and explores the consequences and possible solutions to this problem. Our findings suggest that although adult networks only marginally describe infant FC organization better than chance, misidentification is primarily driven by specific areas. Restricting functional networks to areas with adult-like network clustering revealed consistent within-network FC across scans and throughout development. These areas are also near locations with low network identity variability. Our results highlight the implications of using adult networks for infants and offer guidance for selecting and utilizing functional network models based on research questions and scenarios. HighlightsO_LIPrevious studies primarily investigated age-specific networks in infants, with limited focus on how well adult networks describe infant functional connectivity (FC). C_LIO_LIur analysis identified a subset of areas in infants showing adult-like network organization, where within-network FC shows less age-related variation and higher scan-to-scan reliability. C_LIO_LIThese areas are positioned near locations with low variability in functional network identity in adults, indicating a potential link between developmental sequence and interindividual variability in functional network organization. C_LI

neuroscience↗