Abstract
BACKGROUND: Although an association between brain atrophy and decreased fine motor function has been reported, results from previous studies are inconsistent. We aimed to investigate whether decreased fine motor function is reflected in age- and sex-associated changes in brain structure across the adult lifespan in a large community dwelling cohort study. METHODS: The Rhineland Study is an on-going population-based prospective cohort study in Bonn, Germany. We used cross-sectional data from the first 8318 participants of the Rhineland Study (age range: 30-95 years), who underwent baseline assessments between March 2016 and November 2022. A digital spiral drawing test was utilised to evaluate fine motor skills: tracing precision (deviation area), tracing velocity, and frequency of tremor. Brain volumetric and cortical thickness measures were obtained from 3T T1 MRI scans. The relationship between brain structure and fine motor function was examined with multivariable regression, while adjusting for age, sex, education, smoking status and grip strength. FINDINGS: Smaller volumes and/or thinner cortices in several brain regions were associated with decreased tracing precision (higher tracing deviation area) and higher tremor frequency, including total brain volume (tracing area: β = -0.108, 95% CI = -0.180 to -0.037; tremor frequency: β = -0.077, 95% CI = -0.164 to -0.011), hippocampal volume (tracing area: β = -0.052, 95% CI = -0.089 to -0.015), and cortical thickness of the precentral gyrus (tracing area: β = -0.052, 95% CI = -0.082 to -0.023). Smaller total cerebellar volume (β = 0.061, 95% CI = 0.022-0.100) and total cerebellar grey matter volume (β = 0.060, 95% CI = 0.022-0.099) were both associated with lower tracing velocity. Women performed significantly better on all three dimensions of fine motor function, but age-associated changes in fine motor function did not differ between sexes. INTERPRETATION: Our findings indicate that fine motor function is worse in older adults, and is better in women. Moreover, changes in total brain volume and the thickness of several key motor cortices are robustly related to fine motor function, with the strongest effect for tracing precision. FUNDING: Helmholtz Association DZNE institutional funds, Alzheimer's Association Research Grant (Award Number: AARG-19-616534), China Scholarship Council (Number: 202108080131), and European Research Council Starting Grant (Number: 101041677).