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This Article Full Text Full Text (PDF) All Versions of this Article: 100/4/1813    most recent 01193.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Walker, M. F. Articles by Zee, D. S. PubMed PubMed Citation Articles by Walker, M. F. Articles by Zee, D. S.

Lesions of the Cerebellar Nodulus and Uvula Impair Downward Pursuit

Departments of ¹Neurology, ²Ophthalmology, ³Neurosurgery, ⁴Otolaryngology-Head and Neck Surgery, and ⁵Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland; and ⁶Department of Neurology, Case Western University School of Medicine and the Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, Ohio

Submitted 25 October 2007; accepted in final form 18 July 2008

We studied sinusoidal (SIN) and step-ramp (SR) pursuit in two rhesus monkeys, before and after surgical lesions of the cerebellar nodulus and uvula (Nod/Uv). Eye movements were recorded using the magnetic field scleral search coil method. Pursuit targets were generated by an LCD projector and back-projected onto a tangent screen in an otherwise dark room. After the Nod/Uv lesions, both monkeys showed a reduced eye velocity during downward pursuit (SIN: 42% decrease in M1, 91% decrease in M2; SR: 37% decrease in M1, 85% decrease in M2). For SR, the decrease was seen only for the closed-loop response; initial eye acceleration did not change (P > 0.05). Upward pursuit gains increased for SIN (M1: 9%, M2: 11%); they decreased for SR (M1: 27%, M2: 18%), but to a lesser degree than for downward pursuit. Horizontal pursuit was little changed in M1 but was reduced in one direction in M2, the animal with the larger lesion. The deficit in downward tracking was limited to foveal pursuit; ocular following of random-dot stimuli was retained, even when the target subtended only several degrees. Our findings support a critical role for the Nod/Uv in vertical pursuit, particularly for sustained downward pursuit. Finally, in both monkeys, the lesion increased spontaneous upward ocular drift in the dark (mean prelesion, 1.43°/s; postlesion, 5.92°/s), suggesting a role for the Nod/Uv in holding the eyes still and in the genesis of downbeat nystagmus.