May 2007
Volume 48, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2007
Ablation of the Cerebellar Nodulus and Uvula Selectively Impairs Downward Pursuit
Author Affiliations & Notes
  • M. F. Walker
    The Johns Hopkins University School of Medicine, Baltimore, Maryland
    Neurology,
  • J. Tian
    The Johns Hopkins University School of Medicine, Baltimore, Maryland
    Neurology,
  • X. Shan
    The Johns Hopkins University School of Medicine, Baltimore, Maryland
    Neurology,
  • H. Ying
    The Johns Hopkins University School of Medicine, Baltimore, Maryland
    Ophthalmology,
  • R. J. Tamargo
    The Johns Hopkins University School of Medicine, Baltimore, Maryland
    Neurosurgery,
  • D. S. Zee
    The Johns Hopkins University School of Medicine, Baltimore, Maryland
    Neurology,
  • Footnotes
    Commercial Relationships M.F. Walker, None; J. Tian, None; X. Shan, None; H. Ying, None; R.J. Tamargo, None; D.S. Zee, None.
  • Footnotes
    Support NIH Grant EY01849
Investigative Ophthalmology & Visual Science May 2007, Vol.48, 943. doi:
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      M. F. Walker, J. Tian, X. Shan, H. Ying, R. J. Tamargo, D. S. Zee; Ablation of the Cerebellar Nodulus and Uvula Selectively Impairs Downward Pursuit. Invest. Ophthalmol. Vis. Sci. 2007;48(13):943.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose:: To determine the role of the cerebellar nodulus and uvula in ocular pursuit.

Methods:: In two rhesus monkeys, we used the scleral search coil method to record eye movements during step-ramp pursuit, before and after surgical ablation of the cerebellar nodulus and uvula (Nod/Uv). Monkeys sat in a primate chair with the head immobilized. Each pursuit trial began with fixation of a red target that was back-projected onto a tangent screen in front of the animal. After a random delay, the target stepped horizontally or vertically by 4 deg, then moved smoothly in the opposite direction (20 deg/s) for 1 sec. The animal was rewarded for maintaining fixation of the target. For each experimental session, we calculated pursuit gain by determining the ratio of median slow-phase (desaccaded) eye velocity during the period from 200 to 600 ms after the onset of eye movement to target velocity (all trials pooled for each direction of motion).

Results:: Results were similar in the two monkeys. Median steady-state pursuit gains before the lesions were > 0.7 for horizontal and upward pursuit, and were somewhat lower for downward pursuit (Figure). After the lesion, the gain of downward pursuit decreased by 67 %, of upward pursuit by 2 %, and of horizontal pursuit by 14% (mean of data from both monkeys). After the lesion, both monkeys had downbeat nystagmus in the dark (mean 5.5 deg/s) but not in the light.

Conclusions:: Similar to many humans with cerebellar disease, monkeys with Nod/Uv lesions have a selective deficit of downward pursuit, suggesting a specific role for the Nod/Uv in the facilitation of downward pursuit. A vertical pursuit asymmetry alone does not cause downbeat nystagmus in the light.

Keywords: eye movements: saccades and pursuits 
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