Donders' law in torticollis

We investigated head movements of patients with spasmodic torticollis towar d targets in various directions. These patients, whose severe dystonia was reflected in an abnormal resting head position, appeared to retain a Donder s'-type strategy for the control of the rotational degrees of freedom of th e head. As in normals, rotation vectors, representing head orientation, wer e confirmed to a curved surface, which specifies how head torsion depends o n gaze direction. The orientation of the surface in body coordinates, which was very stereotyped in normals, was different for patients. The same Dond ers surface was found for head movements and for stationary head postures, indicating that the same neural mechanism governs its implementation in bot h tasks. To interpret our results, we propose a conceptual scheme incorpora ting the basal ganglia, which are thought to be involved in the etiology of torticollis, and an implementation stage for Donders' law.