Dopamine replacement therapy does not restore the ability of Parkinsonian patients to make rapid adjustments in motor strategies according to changing sensorimotor contexts

The ability of dopamine replacement to restore rapid motor adjustments in Parkinson's disease (PD) was investigated. Medicated and non-medicated patients performed finger-to-nose movements while simultaneously bending the trunk forward, without vision. Trunk motion was blocked unexpectedly, necessitating rapid adjustments in arm trajectories. Patients exhibited irregular hand paths, plateaus in hand velocity, and prolonged movement times, which were significantly greater in perturbed trials. Medication improved kinematics but perturbation-induced disturbances persisted and did not approximate the levels of non-perturbed trials nor those of controls. Dopaminergic replenishment in PD may therefore have limited restorative benefits for rapid context-specific motor control.