Anatomical correlate of smooth pursuit deficit in patients with cerebellar lesions

Humans are able to stabilize the images of moving targets on the retina by means of smooth pursuit eye movements. After the pontine level, all smooth pursuit pathways pass through the cerebellum. Previous studies gave evidence that two specific lesion sites within the cerebellum cause smooth pursuit disorders: those of the flocculus/paraflocculus and the vermis including lobule VI, VII, the uvula, and the deep cerebellar nuclei. Up to now, there have been only single lesion studies in patients with smooth pursuit disorders. Thus, we used new lesion mapping techniques to determine which cerebellar structures are involved in patients with a deficient smooth pursuit system. Sixteen patients with acute, mainly unilateral cerebellar infarctions and an intact gain of the smooth pursuit system were compared to 11 patients with cerebellar lesions and deficient smooth pursuit gain by means of lesion-mapping imaging. The uvula was found to be the structure commonly damaged in patients with a deficient smooth pursuit gain; it was significantly less involved in patients with intact smooth pursuit system. The pyramid of the vermis and the tonsil were also strongly associated with a deficient smooth pursuit system. The present data give evidence that the uvula is an important anatomical structure within the cerebellar circuitry involved in the generation of smooth pursuit eye movements. Lesions of the uvula might lead to smooth pursuit system deficits.