Coordination of Eye and Head Movements in Cavia Porcellus.

Abstract

The present work provides novel insights into the coordination of vestibular reflexes in the head-unrestrained guinea pig. Eye and head movements were recorded during passive whole body rotations and active head movements. Vestibular signals were subsequently manipulated using galvanic vestibular stimulation to determine the extent to which certain responses are dependent on vestibular afference. The results of this work can be divided into three parts: 1. Guinea pigs exhibit compensatory eye and head movements to passive whole body rotations similar to those in other species. Unlike primates, however, the responses are only weakly compensatory, allowing for significant motion of the eyes relative to space. This difference suggests a lesser need for complete visual stability in the guinea pig and implies therefore, a different purpose for vestibular reflexes. Although there is a high degree of variability in head movement responses to passive whole body rotations, eye movements are always tightly coupled to the resulting movement of the head relative to space. 2. Guinea pigs exhibit anticipatory, compensatory eye movements during voluntary head motion. The response timing and amplitude imply that they are not reflexive in nature and occur in animals with and without an intact vestibular system. This behavior has not been previously reported in animals with an intact vestibular system, and implies different (partially extra-vestibular) neural mechanisms for its generation. 3. Galvanic vestibular stimulation affects both compensatory eye and head movements in the guinea pig. This finding is in contrast to previous ones in primates and implies differences between guinea pig and primate in how afferent vestibular signals are weighted and processed centrally to produce compensatory responses. This work supports the guinea pig as an important animal model in the study of the vestibular system. Additionally, it demonstrates the need for an experimental approach that examines eye and head movements simultaneously as they are reliant on each other for successful vestibular compensation. Finally, the results presented in this work suggest a number of future experiments to improve our understanding of how vestibular afferent signal and extra-vestibular influences interact to produce compensatory eye and head movements.