Disrupted finger force coordination during prehension in mild cognitive impairment

Mild cognitive impairment (MCI) is typically identified through cognitive testing; however, early neurodegenerative changes may disrupt motor coordination before measurable strength loss or overt functional decline occurs. Because the ability to grasp and manipulate objects (i.e., prehension) requires the integration of sensory input, motor planning, and coordinated force production across digits, it serves as a sensitive window into early neural dysfunction. In this study, we examined multi-level motor control during a steady prehension task in 66 older adults with and without MCI. Using a hierarchical variability decomposition (HVD) framework, we distinguished between real-time error regulation and the consistency of motor planning. Compared with healthy controls, individuals with MCI exhibited impaired coordination between fingers, reflected by less effective force sharing and reduced stability across trials. Notably, these deficits occurred despite preserved variability in individual finger forces, indicating a disruption in how forces are organized across digits rather than a loss of single-digit control. These impairments were accompanied by greater force-targeting errors and poorer functional hand performance, despite preserved maximal grip strength. Together, these findings demonstrate that MCI involves a hierarchical breakdown in coordinated finger control, suggesting that quantitative hand-function assessment may provide a robust neuromechanical marker for detecting early-stage neurodegeneration.