Utricular sensitivity and preponderance assessed by the unilateral centrifugation test

Utricular sensitivity and preponderance of the right or left utricle can be assessed by means of the unilateral centrifugation test. In this test, subjects are rotated about an earth vertical axis at a velocity of 400 degrees per second. During the ongoing rotation, the subject is gradually translated 4 cm first to the right, and then to the left, along an interaural axis, to a position at which one utricle becomes aligned with the axis of rotation, and at this point is subjected only to gravitational forces. At this eccentric position, the contralateral utricle is exposed to the combination of gravity and a centrifugal acceleration of 0.4g, corresponding to an apparent roll-tilt of 21.7 degrees. This stimulus induces ocular counterrolling (OCR), which is measured on-line using three-dimensional video-oculography (VOG). We observed that ocular counterrolling appears as a linear function of the gravito-inertial acceleration tilt of the head centre (GIA(HC)) during the lateral translation. We present a theoretical model for this linear relationship that contains two parameters: 1) the slope of the linear regression is a measure for the utricular sensitivity and 2) the intercept of the linear regression is a measure of the preponderance of the right or left utricle. The strength of the model is supported by data obtained from 28 healthy subjects and 14 patients with unilateral vestibular deafferentiation (UVD) due to acoustic neuroma surgery.