IMPAIRMENTS OF MOVEMENT KINEMATICS IN PATIENTS WITH HUNTINGTONS-DISEASE - A COMPARISON WITH AND WITHOUT A CONCURRENT TASK

This study aimed to quantify the efficiency and smoothness of voluntar y movement in Huntington's disease (HD) by the use of a graphics table t that permits analysis of movement profiles. In particular, we aimed to ascertain whether a concurrent task (digit span) would affect the k inematics of goal-directed movements. Twelve patients with HD and thei r matched controls performed 12 vertical zig-zag movements, with both left and right hands (with and without the concurrent task), to large or small circular targets over long or short extents. The concurrent t ask was associated with shorter movement times and reduced right-hand superiority. Patients with HD were overall slower, especially with lon g strokes, and had similar peak velocities for both small and large ta rgets, so that controls could better accommodate differences in target size. Patients with HD spent more time decelerating, especially with small targets, whereas controls allocated more nearly equal proportion s of time to the acceleration and deceleration phases of movement, esp ecially with large targets. Short strokes were generally less force in efficient than were long strokes, especially so for either hand in eit her group in the absence of the concurrent task, and for the right han d in its presence. With the concurrent task, however, the left hand's behavior changed differentially for the two groups; for patients with HD, it became more force efficient with short strokes and even less ef ficient with long strokes, whereas for controls, it became more effici ent with long strokes. Controls may be able to divert attention away f rom the inferior left hand, increasing its automaticity, whereas patie nts with HD, because of disease, may be forced to engage even further online visual control under the demands of a concurrent task. Patients with HD may perhaps become increasingly reliant on terminal visual gu idance, which indicates an impairment in constructing and refining an internal representation of the movement necessary for its. effective e xecution. Basal ganglia dysfunction may impair the ability to use inte rnally generated cues to guide movement.