Among the sensory modalities available to vertebrate animals, vision is most advantageous for it provides information in a wide three dimensional space with high acuity. Thus, redirecting our eyes to retain images of objects of interest on the fovea while we are in motion becomes a crucial motor function. The nervous system solves this problem by using short-latency vestibulo-ocular reflexes (VORs) to generate eye movements that compensate for angular (angular VOR or AVOR) or linear (linear VOR or LVOR) motions of the head. Sensory inputs driving the AVOR and LVOR arise from different labyrinthine sensors (the semicircular canals and otolith organs, respectively). This means that, if as existing evidence suggests, the compensatory LVOR is built upon the phylogenetically older AVOR brainstem circuitry and thus both share a common premotor pathway, the linear acceleration signals coded by otolith afferents must be transformed to match the velocity-position signals generally observed on AVOR neurons. Likewise, the three-dimensional spatial directions of angular and linear motion signals must be brought into alignment. Complexity arises since different patterns of eye movements are evoked in response to high frequency linear motions, which generate translational LVORs, and to low frequency linear motions, which generate orienting (tilt) responses. Alternatively, AVOR, LVOR and tilt-related signals might be carried via separate VOR pathways converging upon extraocular motoneurons. Another unresolved issue is that the bilateral organization of otolith and canal sensory epithelia is quite different, and thus the bilateral """"""""push-pull"""""""" mechanism in AVOR may not apply to LVOR. The four aims that follow are designed to address these and other related questions regarding coordinated VOR responses to angular and linear head motions.
These aims are: Identify the synaptic connections of VOR neurons that project to oculomotor nuclei and receive direct VIIIth nerve inputs. Examine the spatial and temporal tuning properties of VORns during the AVOR, LVOR, smooth pursuit and fixation of targets at various viewing distances. Examine the bilateral organization of utriculus related inputs to VOR neurons. Examine responses of VORns during static tilts and low frequency earth-horizontal rotations that produce comparable acceleration to translations and examine how translation and tilt related signals are distributed in VOR pathways.
| Chen-Huang, Chiju; Peterson, Barry W (2010) Frequency-dependent spatiotemporal tuning properties of non-eye movement related vestibular neurons to three-dimensional translations in squirrel monkeys. J Neurophysiol 103:3219-37 |
