Object-directed actions in Parkinson’s disease: Observation and imitation of hand movements

Action observation and imitation may facilitate movement and increase functional independence in Parkinson’s disease (PD). People with PD have been found to imitate intransitive actions in a similar manner to neurologically healthy older adults, but their ability to imitate object-directed hand movements has not been investigated using kinematic measures. The present study examined observation and imitation of object-directed hand movements in 18 participants with PD compared to 21 neurologically healthy age-matched control participants. Participants observed and immediately imitated sequences showing a human hand reaching for and transferring an object between horizontal positions. Both participants with PD and age-matched controls significantly modulated the vertical amplitude of their finger movements when imitating elevated vs. direct trajectories. Movements were lower in vertical amplitude and faster when imitating the reaching segment of the observed movement than the transfer segment. Eye-tracking revealed significant effects of predictability of the movement sequence on saccade amplitude in the control group, specifically when observing elevated movements, but no effects of predictability on eye movements were found for the PD group. This study provides quantitative evidence indicating that people with mild to moderate PD can imitate the kinematics of object-directed hand movements, although their observation and prediction of such movements may be somewhat altered. These findings suggest that interventions based on observation of object-directed actions may facilitate daily activities in PD through imitation of movement kinematics.