Do patients with neglect show abnormal hand velocity profiles during tactile exploration of peripersonal space?

It has been suggested that the movement impairments experienced by patients with neglect are not restricted to spatial disorders, but also affect high er-order kinematics (velocity and acceleration) to the extent that movement s towards the neglected side are slower than movements away from it. In a r ecent study, we could not confirm this hypothesis, but found that patients with unilateral neglect exhibited no distinct direction-specific deficits i n hand velocity when performing goal-directed reaching movements. Here we i nvestigated whether neglect patients might reveal direction-specific defici ts during exploratory hand movements. Six patients with left-sided neglect and six age-matched healthy control subjects scanned with their right hands the surface of a large table searching for a (non-existent) tactile target . Movements were performed in darkness. Time-position data of the hand were recorded with an optoelectronic camera system. Median activity of the pati ents' exploratory hand movements was shifted to the right (Karnath and Pere nin 1998), Hand trajectories were partitioned into sections of leftward/rig htward or, along the sagittal plane, into sections of near/far movements, F or each movement section average and peak velocities were computed. The pat ients' hand movements were bradykinetic when compared with the control grou p. However, we found no evidence that average or peak velocities of leftwar d intervals were systematically lower than during rightward motion. Directi on-specific deficits in velocity were also not observed for movements to an d away from the body (sagittal plane). In conclusion, we found evidence for general bradykinesia in neglect patients but not for a direction-specific deficit in the control of hand velocity during exploratory hand movements.