A quantitative study of eye and head movements during smooth pursuit in patients with cerebellar disease

Eye and head movements were analysed during smooth pursuit in 16 patients with various forms of cerebellar disease. Smooth pursuit gain was reduced across all frequencies and velocities of target motion for the patient group as a whole, during both sinusoidal and pseudo-random target motion. The graded breakdown in the pursuit response, as pseudo-random target motion became less predictable, was of a similar magnitude in patients and controls, implying that the predictive pursuit mechanisms were intact in these patients. During head-free pursuit, when vestibulo-ocular reflex (VOR) suppression was necessary, performance was not significantly different from that observed during head-fixed pursuit in the patient group. This finding is similar to that noted in control subjects, and is consistent with the observation that the VOR gains associated with head movements in darkness were similar in the patient and control groups. The deficits in pursuit and VOR suppression in patients with cerebellar disease therefore represent a decrease in gain in the closed-loop visual feedback pathways with apparent sparing of the predictive pathways.