S161. Eye-hand coordination in hereditary spinocerebellar degeneration

Abstract

Gaze and hand movements are known to be closely linked in daily actions (eye-hand coordination), and the cerebellum is implicated in the control of this eye-hand coordination. There are negative reciprocal interactions between the eye and hand movements when patients with cerebellar dysfunction perform a target tracking task. We devised a system which is capable of simultaneously recording the trajectory of hand and eye movements when subjects performed a visually guided reaching task. The aim of this preliminary study was to investigate how cerebellar dysfunction affects the coordination. Subjects were 8 patients with hereditary spinocerebellar degeneration (SCA6 or SCA31) with pure cerebellar symptoms and 9 age-matched normal controls. A video-based eye tracker recorded eye movements while a touch panel recorded the trajectory of finger movements while performing the visually guided reaching task. A fixation spot was presented in the center of the touch panel, which the subjects fixated and touched with the index finger. At a random interval, this fixation spot moved to a peripheral position, selected from positions at an eccentricity of 10 or 20 degrees (in 8 directions separated by 45 degrees), to which the subjects were to move their fingers by sliding their fingers over the monitor. The subjects also performed a visual guided saccade task, in which they made a saccade to the peripheral target without moving the finger. In SCA patients, trajectory of both eye and finger showed hypermetria in comparison with normal controls. Superimposed trajectories of saccades showed a wider distribution than that of finger movements, which implied that the variability of eye movements did not directly translate into that of the hand movements. In most trials, the eyes preceded the finger movements to the target location, and was locked at the target location until the hand was reached the target location. The interval between onsets of the hand and eye movements was larger for SCA patient than for normal subjects. This wider separation between the hand and eye onset was due to the eyes moving to the targets in multiple steps of saccades with changing direction and the hand did not start before the eyes reached the vicinity of the target. Eye-hand coordination was disrupted in hereditary spinocerebellar degeneration. In SCA patients, the multistep saccade and saccades that changed direction toward the target prevented gaze locking at the target required for eye-hand coordination, and led to increased interval between the saccade onset and finger onset.