A model of human aiming movements applied to Parkinson's disease

Healthy control subjects and Parkinsonian patients with and without l-DOPA medication were tested in a motor paradigm. The subjects were instructed to aim with the forearm as fast and as accurately as possible to the illuminated target. A quantitative dynamic model for planning and execution of voluntary aiming movements is developed. The proposed 'motor model' reproduces Parkinsonian symptoms and the therapeutic effects of the drug. The proposed model implies that the basal ganglia store movement and limb specific parameters which are necessary for the control of voluntary aiming movements. The model is contrasted against analytic concepts of motor control. Analytic concepts assume that movements are planned in space coordinates and then transformed to neural activities corresponding to the muscle force. In contrast, the neuronal activities simulated in the proposed 'motor model' can not be described by the terms 'planned trajectory', 'muscle force' or similar terms but suggest a more abstract dynamic concept.