Vestibulo-ocular reflex in eccentric rotation in squirrel monkeys

In addition to angular acceleration, eccentric rotation (ECR) imparts linear acceleration to the head positioned eccentric to the axis of rotation. Using ECR in squirrel monkeys, the effects of otolith organ stimulation by linear acceleration on vestibulo-ocular reflex (VOR) gain were investigated. With the animal's head facing away from the rotation axis, ECR significantly enhanced VOR gain over that seen in centric rotation (CR) at 1.0 Hz, but not at 0.5 Hz. However, no enhancement of VOR gain at 1.0 Hz was observed in eccentriclateral rotation when the animal faced tangentially. After bilateral ablation of the otolith organs (sacculectomy and utricular neurectomy), the ECR did not increase VOR gain, even at 1.0 Hz. In animals in which the lateral and posterior semicircular canals were plugged bilaterally, horizontal sinusoidal eye movements were induced by ECR at 1.0 Hz; no clear compensatory eye movement occurred during CR at 1.0 Hz. These findings demonstrate that during ECR, tangential acceleration along the interaural axis stimulates the utricular maculae, inducing horizontal eye movements in addition to those induced by the semicircular canal, thus resulting in an enhancement of VOR gain. Our results also suggest synergistic interactions of the otolith organs and semicircular canals. We conclude that ECR is a useful clinical test of the function of the otolith organs.