Vestibulo-ocular reflex pathways in internuclear ophthalmoplegia

We measured the vestibule-ocular reflex (VOR) during head impulses in a pat ient with right-sided internuclear ophthalmoplegia. Head impulses are rapid , passive, high-acceleration, low-amplitude head rotations in the direction of a particular semicircular canal (SCC). Adduction of the right eye was a bnormally slow during right lateral SCC head impulses. The VOR during left posterior SCC impulses was severely deficient in both eyes, but the VOR dur ing left anterior SCC impulses was only slightly deficient. We suggest that the vertical vestibule-ocular pathways in humans are connected in SCC-plan e coordinates, not the traditional roll and pitch coordinates, and that ant erior SCC signals do not travel exclusively in the medial longitudinal fasc iculus.