How a once-controversial idea is advancing understanding of Parkinson’s disease

Parkinson's disease (PD) can hinder skilled actions, but its impact on rhythmic, bimanual tasks remains unclear. To investigate this, researchers conducted a bimanual hand-over-hand string-pulling task, which involves reaching, grasping, pulling, pushing, and releasing. Of the participants, nine had PD, 16 were older adults, and 10 were young adults.

In the real task, along with a pantomimed version, the team employed video analyses to measure whole-body movement speed, upper-limb kinematics, and hand and finger shaping. Using machine-learning classification, they identified which movement components differentiated the participants. Those with PD demonstrated slower movement speed, a smaller hand workspace, and less hand and finger shaping, while older adults showed intermediate values.

Despite these differences, all participants grasped the string with a power grip. However, those with PD showed reduced rotary arm and wrist movements, and lacked the arpeggio-like sequential finger movements observed during grasp and release. During pantomiming, those with PD moved faster and made larger hand movements, but their grasp-related hand opening and finger sequencing were reduced or absent.

These findings suggest that PD affects multiple components within a complex movement system. Additionally, the study reveals that task demands can modify movement organization: real string-pulling requires the formation and release of a power grip, while pantomiming does not.