The reach-to-grasp movement in Parkinson's disease before and after dopaminergic medication

The aim of the present study was to assess the effects of dopaminergic medication on the organisation of the reach-to-grasp movement in Parkinson's disease. A three-dimensional kinematic system (ELITE, B|T|S| Italy) was used to record reach-to-grasp movements to objects of either small (0.7 cm) or large (8 cm) diameter placed at a reaching distance of either 20 or 30 cm. Vision of the reaching limb and target was also manipulated. Parkinson's disease participants (N =14) were assessed in `OFF' (12 h without medication) and `ON' (1±2 h post-administration of medication) states. In the `ON' state, movement duration and the time spent in arm deceleration were significantly less than in the `OFF' state. The amplitudes of peak reaching velocity, acceleration and deceleration were all higher in the `ON' than in the `OFF' state. Further, in the `ON' state, the acceleration profile no longer exhibited small irregular adjustments, the number of significant correlations between parameters measured from the transport and manipulation components was greater, and the movement was more direct in both the mediolateral horizontal and vertical planes. These results indicate that dopaminergic medication is of benefit in reducing bradykinesia and in fine-tuning kinematic parameterisation of a selected reach-to-grasp action.