Mechanisms of vestibulo-ocular reflex (VOR) cancellation in spinocerebellar ataxia type 3 (SCA-3) and episodic ataxia type 2 (EA-2)

Carlos R. Gordon, Avi Caspi, Ronen Levite, Ari Z. Zivotofsky

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

13 Scopus citations

Abstract

The vestibulo-ocular reflex (VOR) mechanism triggers eye movements as a result of head motion in order to keep gaze stationary relative to the world. However, in order to shift the direction of the gaze along with head motion, the VOR mechanism must be overridden ("cancelled"). Two mechanisms have been proposed to explain this cancellation: a reduction of the VOR gain or activation of smooth pursuit (SP) eye movements in the opposite direction. We studied VOR cancellation using the magnetic search coil in six spinocerebellar ataxia type 3 (SCA-3) and four episodic ataxia type 2 (EA-2) patients, conditions that are known to have degraded SP but different degrees of VOR impairment. Abnormal VOR was found in two of the four EA-2 patients and all of the SCA-3 patients. All subjects possessed residual VOR, although when tested using head thrusts it was almost negligible in the SCA-3 patients. The EA-2 patients showed essentially no SP and the SCA-3 patients had poor SP. However, for all patients, the gain during VOR cancellation was comparable to normals. These results provide additional evidence that SP cancellation of the VOR cannot be the sole mechanism utilized in overriding the VOR in these patients.

Original languageEnglish
Title of host publicationUsing Eye Movements as an Experimental Probe of Brain function A Symposium in Honor of Jean Buttner-Ennever
PublisherElsevier
Pages519-525
Number of pages7
ISBN (Print)9780444531636
DOIs
StatePublished - 2008

Publication series

NameProgress in Brain Research
Volume171
ISSN (Print)0079-6123

Bibliographical note

Funding Information:
This study was partially supported by the German-Israel Foundation (GIF) for Scientific Research and Development and the Gonda fund for Brain Research.

Keywords

  • VOR gain
  • eye-head tracking
  • head thrust
  • magnetic search coil
  • saccadic tracking
  • smooth pursuit

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