Age-specific relationship between the modulation of brain dynamics in response to task demands and bimanual performance.

While prior research has largely focused on mean Blood Oxygen Level-Dependent (BOLD) activation to understand age-related differences in bimanual coordination, BOLD variability - a metric that captures fluctuations in brain activity -, has been overlooked. Hence, the current study examined how age affects BOLD variability, specifically BOLD standard deviation (BOLD SD), and its modulation with task demands during a bimanual task. Twenty-two younger and twenty-three older adults performed three task conditions of increasing complexity while undergoing functional magnetic resonance imaging (fMRI).Older adults exhibited higher BOLD SD in cerebellar lobule VIIIb and greater modulation across task conditions in both sensorimotor and cerebellar regions. Modulation of BOLD variability predicted task performance in an age- and region-dependent manner: in younger adults, reduced modulation in sensorimotor and visuospatial areas correlated with better performance, whereas in older adults, increased modulation in the inferior and superior parietal lobules was linked to higher performance. Across groups, better outcomes were predicted by greater modulation in the middle occipital gyrus but less in the cerebellar Crus I. These findings underscore an age-related shift in the neural dynamics underpinning motor adaptability with aging, pointing to increased BOLD variability modulation as a potential marker of compensatory reorganization in late adulthood.