Prehension with the ipsilesional hand after unilateral brain damage

Sensorimotor deficits in the hand ipsilateral to a brain lesion have been reported in different motor tasks. We evaluated performance of the ipsilesional hand in 12 patients with either left (LBD) or right brain damage (RBD) by kinematic analysis in order to precisely characterize possible deficits in the two components of prehension (transport and grasp). Both patient groups exhibited performance deficits in the main kinematic parameters, e.g., reduced velocity of the transport component and prolonged movement time. However, while LBD patients showed a more general slowing, RBD patients prolonged in particular the last phase of the movement toward the object. We suggest that relevant visuospatial representations and the adequate mapping of motor processes may be impaired after RBD. In contrast, LBD caused a more unspecific disturbance pattern, supporting the view that the precise parameterization of motor programs is impaired. Maximum grip aperture was normal in both patient groups. However, since aperture could be biased by slowed movement, the notion that the grasp component was preserved remains speculative. The patient's ability to scale the maximum velocity of the transport component to adapt to changes in movement amplitude and to scale the maximum hand aperture of the grasp component to adapt to object size was preserved in both groups. Thus both hemispheres can have competence for this scaling mechanism.