The vestibular system is crucial in maintaining equilibrium and orientation in space. One of its major functions is the vestibulo-ocular reflex (VOR). The VOR generates compensatory rotations of the eyes during head movements in order to maintain binocular fixation on visual targets, and therefore a stable retinal image. We focus on the VOR because it is the most direct and accessible behavior from which mechanistic inferences about vestibular function can be derived. The VOR is activated by two kinds of head acceleration; angular (the AVOR), driven by the semicircular canals, and linear (the LVOR), driven by the otoliths. Linear stimuli include two forms, translational motion and tilt relative to gravity. Each drives the LVOR in specific ways. An important feature of the VOR is its ability to adaptively modify performance in response to prolonged visual-vestibular mismatch during head movements. However, this phenomenon has only been demonstrated in the AVOR. In addition, the VOR is modulated by instantaneous viewing conditions (e.g. target distance and gaze), more so in the LVOR than the AVOR. The proposed experiments will determine how canal and otolith inputs interact to generate, and adaptively maintain, behaviorally useful ocular responses during angular, linear, and complex head movements. New techniques will be employed to study the LVOR and its relationships with the AVOR and vision over a broad range of motion profiles and fixation contexts. Relationships between translational and tilt LVORs will be elucidated. Novel adaptive mechanisms will be explored and characterized. We will determine whether plasticity in the AVOR and LVOR share neural elements. Specific endorgan lesions will be employed to directly assess the origin of VOR behaviors, and to elucidate unique adaptive processes that restore function.
