The primary goal of this subproject is to characterize the otolith-ocular responses elicited by off-vertical axis rotation (OVAR) in normal, peripheral lesioned, and central lesioned humans. The eye movement responses will be obtained with dual scleral search coils during per-rotatory and post-rotatory periods of OVAR using three-dimensional measurement techniques that have recently been incorporated into the P.I.?s laboratory. A second major goal is to characterize the interaction between vestibular stimulation and volitional eye movements in normal human subjects, with the ultimate objective to determine if vestibular disturbances produce deficits in visual-vestibular interactions. The first specific aim consists of two parts. First, the subproject seeks to determine if the reorientation of the eye rotation vector that is aligned with gravity during OVAR post-rotatory responses will be asymmetric in peripheral lesioned patients. In normal primates, the slow phase eye velocity during OVAR post-rotatory responses re-orients to be aligned with gravity regardless of head position due to inertial otolith signals. In nerve lesioned patients, it is hypothesized that the reorientation will be reduced or absent when the lesioned ear is placed downward. Second, the subproject will address whether the per-rotatory OVAR responses have abnormal eye movement components in lesioned patients as compared to normals. The second specific aim will use the same testing conditions for per- and post-rotatory OVAR responses in cerebellar damaged patients to examine possible differences in eye rotation vector re-orientation and 3-D otolith ocular reflex organization. The third specific aim will examine saccadic and smooth pursuit eye movements made during concurrent head rotations. The three dimensional organization of these volitional eye movements will be characterized during both earth-vertical axis and constant velocity OVAR rotations to compare canal versus otolith visual-vestibular interactions.
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