Response of Vestibular Nerve Afferents Innervating Utricle and Saccule During Passive and Active Translations

Department of Physiology, Aerospace Medical Research Unit, McGill University, Montreal, Quebec, Canada Submitted 22 September 2008; accepted in final form 24 October 2008 The distinction between sensory inputs that are a consequence of our own actions from those that result from changes in the external world is essential for perceptual stability and accurate motor control. In this study, we investigated whether linear translations are encoded similarly during active and passive translations by the otolith system. Vestibular nerve afferents innervating the saccule or utricle were recorded in alert macaques. Single unit responses were compared during passive whole body, passive head-on-body, and active head-on-body translations (vertical, fore-aft, or lateral) to assess the relative influence of neck proprioceptive and efference copy-related signals on translational coding. The response dynamics of utricular and saccular afferents were comparable and similarly encoded head translation during passive whole body versus head-on-body translations. Furthermore, when monkeys produced active head-on-body translations with comparable dynamics, the responses of both regular and irregular afferents remained comparable to those recorded during passive movements. Our findings refute the proposal that neck proprioceptive and/or efference copy inputs coded by the efferent system function to modulate the responses of the otolith afferents during active movements. We conclude that the vestibular periphery provides faithful information about linear movements of the head in the space coordinates, regardless of whether they are self- or externally generated. Address for reprint requests and other correspondence: K. E. Cullen, Aerospace Medical Research Unit, 3655 Drummond St., Montreal, Quebec H3G 1Y6, Canada (E-mail: Kathleen.cullen{at}mcgill.ca )