Three dimensional eye-head coordination after unilateral inactivation of the interstitial nucleus of Cajal (INC) in the primate

The interstitial nucleus of Cajal (INC) has previously been shown to control both torsional and vertical eye position and head posture. This thesis examines the coordination of eye and head movements during reversible pharmacological INC inactivation by recording 3-D eye and head movements in 3 monkeys. Torsional drift (about the naso-occipital axis) was observed in the eye and head, followed by progressive clockwise/counterclockwise tilts after left/right INC inactivation. Vertical and horizontal drift and tilts were not consistently observed although vertical drift of the eye was dependent on both vertical position of the eye and the magnitude of the previous vertical saccade. Ocular counterroll and torsional vestibulo-ocular reflex (VOR) became dysfunctional. These results suggest that eye and head deficits after INC inactivation are completely interdependent in a complex fashion during fixation, gaze shifts, and VOR, and closely resemble the deficits in spasmodic torticollis.