[A tridimensional study of lateral grasping and pointing in spatial neglect]

The aim of this study was to analyze the ipsilateral upper limb and head kinematics in patients presenting with spatial neglect, using pointing and grasping to object. Four patients were included and compared to an equivalent number of normal subjects. Head, shoulder, and wrist movements were recorded using a three-dimensional VICON system. Objects to be pointed or grasped were localized in the right or left space facing the subject. Patients presented with a reduction in the mean wrist velocity, which was more obvious when directed to the left side, reduction in the peak velocity, and a severe increase of the time between the peak velocity and the end of the movement. The amplitude and mean velocity of left head movements were comparable in both groups. The analysis of the intersegmental co-ordination showed that the sequence of activation of corporeal segments was similar in patients and controls: head movement, shoulders rotation, upper limb extension. Co-ordination between head and wrist movements was assessed using the cross-correlation method. An increase in time lag and a reduction in crossed correlations between the head and wrist movements was observed in leftward movements of neglect patients, but the co-ordination between the shoulder and wrist movements was preserved. Thus, we demonstrated a global disorder of intentional movements in patients, which was relatively similar in pointing and grasping to object, and predominated on the approach phase, which is associated to important visuo-motor adjustments. This study also demonstrated desynchronization of head and wrist movements, which can be an important problem in neglect patients.