Longitudinal changes in hand dominance and manual dexterity in normal aging and mild cognitive impairment (MCI): a kinematic study.

Introduction: Decrements on hand dominance in older populations, including neurodegenerative conditions, have been reported cross-sectionally. At present, no longitudinal research on this issue is available. Methods: To address this research gap, we conducted a detailed kinematic analysis of unimanual movements of the dominant and non-dominant hands in 16 patients with mild cognitive impairment (MCI) (M age = 69.3 yrs) and 20 healthy controls (HC) (M age = 69.9 yrs) at two points in time with an averaged time interval of 4.5 years between evaluations (3.5 yrs. for HC; 5.35 yrs. for MCI). The inserting pins task from the Purdue Pegboard Test was recorded with a 2D motion capture system (Vicon Motus). Linear and angular velocities, as well as path length together with their coefficients of variation were calculated for specific actions (i.e., reaching, grasping, transport and inserting) and laterality indices (LI) were computed. Results: At time 1, only MCI patients displayed symmetric movements. At time 2, no group differences in LIs were observed as the HC group also developed symmetric hand dominance while MCIs preserved symmetric hand dominance. The present study is the first one to demonstrate longitudinally the presence and development of reduced manual asymmetry in two groups of older adults with and without cognitive impairment. Discussion: These findings are fundamental to document the development of symmetric hand performance in old age, which most likely represents a behavioral adaptation to normal neurophysiological constraints caused by the wear and tear of the neuromuscular system, rather than being solely the result of pathology. However, conditions like MCI that are superimposed upon normal senescence processes appear to accelerate the development of reduced manual asymmetry.