Age-group differences in diffusion MRI characteristics of cortico-cerebellar tracts and their association with bimanual performance.

Abstract

Introduction: Aging is associated with alterations in white matter structure and decline in bimanual performance. These parallel changes may be interrelated, as previous studies have linked cerebral white matter properties to both motor and cognitive function. The cerebellum plays a central role in complex motor coordination and higher-order processes, yet age-related differences in cortico-cerebellar pathways remain insufficiently understood. This study therefore examined two major cortico-cerebellar tracts - the dentato-rubro-thalamo-cortical tract (DRTT) and the cortico-ponto-cerebellar tract (CPCT) - to assess age-related differences in white matter properties and their association with bimanual motor performance.

Methods: Diffusion Magnetic Resonance Imaging data from 46 younger and 46 older healthy adults were analyzed using a state-of-the-art fixel-based analysis approach to derive fiber-specific metrics reflecting micro- and macrostructural axonal properties.

Results: An overall reduction in fiber density and cross-section was observed in older adults, primarily driven by macrostructural differences; alongside localized increases in these structural properties in specific regions. No significant associations were found between cortico-cerebellar white matter properties and bimanual motor performance.

Discussion: These findings corroborate the general patterns of age-related white matter decline while underscoring the importance of within-tract analyses. Although cortico-cerebellar pathways demonstrate age-related structural differences, their contribution to age-related alterations in bimanual coordination performance in healthy aging may be limited or obscured by tract-level averaging masking regional effects and the multifactorial nature of bimanual motor coordination, which reflects the interaction of distributed neural and peripheral systems. The observed regional increases of fiber-specific measures in older adults may reflect age-related adaptations. Yet, their functional significance remains uncertain and warrants further investigation.