Transaural linear vestibulo-ocular reflexes from a single utricle

To clarify the directional sensitivity of a single utricle with respect to the transaural linear vestibule-ocular reflex (L-VOR) we studied seven patients before and after vestibular neurectomy. Patients were seated upright in an electrically powered car running on a linear track. Transaural acceleration steps of 0.24 g were applied randomly to the left and right in the dark The slow phase velocity of the L-VOR was measured from the average of the induced compensatory eye movements. L-VOR asymmetry was calculated as (\R-L\/\R+L\ x 100) and is < 13% in normals. Before surgery, responses were mostly symmetrical. One week after surgery, however, all patients had diminished or absent responses with medial acceleration of the remaining utricle. Asymmetries averaged 65% after correction for spontaneous nystagmus. Our findings indicate that afferents for the L-VOR originate from the lateral region of the macula where hair cells with ipsilateral on-directions are located.