The proposed research program will study the contribution of the otolith vestibular organs to the vestibulo-ocular reflex. The vestibulo-ocular reflex rotates the eyes counter to any head rotation in order that visual fixation remains constant and vision unblurred. The vestibular canals produce the vestibulo-ocular reflex during head motion that is horizontal with respect to the earth. When head rotation is not horizontal, the gravity sensitivity of the otoliths can improve the vestibulo-ocular reflex by adding to it a signal that reliably indicate head tilt. We will do four series of experiments in cats to explore the otolith vestibulo- ocular reflex. 1) The vestibulo-ocular reflex will be measured quantitatively for three dimensions of rotational motion. Reflex action will be compared for rotations that are identical with respect to the cat but with the animal in different gravity orientations so that otolith contribution to the reflex varies or is absent. Improved vestibulo-ocular reflex stabilization of the eyes in the presence of gravity tilt is evidence for otolith input to the vestibulo-ocular reflex. 2) The vestibulo-ocular reflex will be measured quantitatively in three dimensions in cats that have had their vestibular canals inactivated by plugging the canal ducts. The remaining vestibulo- ocular reflex is produced by the otolith organs. 3) The contribution of the otoliths to adaptive capacity of the vestibulo-ocular reflex will be assessed by comparing adaptive alteration of the vestibulo-ocular reflex direction during vestibular stimulation that excites otoliths or only canals. Vestibulo-ocular reflex direction adaption will be produced by coupling vestibular rotation to visual world motion in a conflicting direction. 4) The responses of brainstem vestibular neurons to rotational stimulation of otoliths and canals will be recorded to explore the convergence of vestibular signals on the vestibulo-ocular reflex pathway. Responses will be recorded during the stimuli described above for reflex tests, in search of responses that could contribute to the observed canal and otolith vestibulo-ocular reflex responses. The finding from the proposed research will add to our understanding of the brain reflex mechanism that stabilize the direction of vision and increase our knowledge of the function of the gravity sense responses of the otolith organs of the vestibular apparatus.
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