Dissociation in the neural control of single-joint and multi-joint movements in the thalamic ataxia syndrome

We report a patient presenting with a right thalamic ataxia syndrome following a hemorrhage located in the left lateral and posterior thalamus. We investigated the fast goal-directed movements of the wrists (single-joint movements) and the fast pointing movements in the upper limbs (multi-joint movements). On the right side, single-joint movements were markedly hypermetric and characterized by an asymmetry in kinematics, an abnormality of ballistic movements which is considered to be a fundamental cerebellar disorder. By contrast, rapid multi-joint movements were only very slightly impaired. These results suggest that ballistic movements of the wrist are under the strong influence of the cerebello-thalamo-cortical pathway, while rapid pointing multi-joint movements in upper limb are mostly influenced by another pathway emerging from the lateral cerebellum, possibly the dentato-rubral or the dentato-reticular projections in the brainstem. The roles of these neuroanatomical pathways in the control of fast single-joint and multi-joint movements are discussed.