Intention tremor during manual aiming: a study of eye and hand movements

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Abstract
A ccurate goal-directed movements toward a visual target require a precise coordination of both the oculomotor and limb motor systems. Intentio n tremor and eye movement deficits are frequently observed in multiple sclerosis (MS). The goal of this study was to examine the characteristics of intentio n tremor and simultaneously produced eye movements during rapid goal-directed movements. Eye and hand movements were synchronously measured in 16 MS patients with intentio n tremor and 16 control subjects. Manual performances of the patient group were character ized by a delayed onset, slower executio n and aiming inaccuracies. In line with the clinically defined picture of intention tremor, differences between patients and control subjects were most pronounced toward the end of the movement. Dependent variables were obviously greater in MS patients compared with control subjects, and correlated well with clinical outcome measures. The application of an inertial load to the limb did not show any effect on intention tremor. In addition to impaired limb coordination, evidence has been found that eye movements, too, were abnormal in patients compared with control subjects. Moreover, eye and hand movement deficits seemed to be closely related, suggesting a common underlying command structure. Inaccurate eye movements were likely to hamper an accurate motor performance of the hand.