Impairments in Estimation of Target Velocity in SCA 6

Objective: Perception during visual motion is a fundamental function for the equilibrium system. Neural substrates for these systems are still incompletely known. We examined the role of cerebellum for those systems in Spinocerebellar ataxia type 6 patients. Method: Seven SCA6 patients and 7 age-matched normal controls participated in this study. Two tasks were tested. Task 1 examined subjects’ ability to estimate the timing of a target movement indicated by a finger movement. Task 2 examined the ability to match the remembered velocity of visual pattern movement. Results: In Task 1, when the target was always visible, the difference between the 2 groups was not significant at 2°/s and 5°/s of target movement. At 8°/s, there was significant difference between them. During the 50% target blanking condition, the patients showed lower successful ratios at 5°/s and 8°/s, respectively. In Task 2, when both subject groups fixated a stationary spot, there was no significant difference between the two groups at 2°/s and 5°/s. However, at 8°/s, the difference was significant. When a fixation spot was not presented, the difference was significant at all three velocities. Conclusion: Most SCA6 patients exhibited a larger variability in their timing estimation, and their estimations significantly lagged compared with controls. The present findings shed light on the mechanisms of estimation of target velocity and timing of movement initiation and support the conclusion that the cerebellum is involved in these functions.