The overall goal of the proposed experiments is to describe the neuronal structure-function relationships of spatially and temporally coordinated eye and head movements by analyzing their intrinsic reference frame systems in both functional and phylogenetic contexts. The experimental paradigms include the spatial organization and central representation of the visual input to the olivo-cerebellar system, the functional anatomy of eye-head coordination, and the morphology and physiology underlying horizontal and vertical compensatory and voluntary eye movements. These objectives will be addressed in the following five specific aims. 1) The spatial organization of optokinetic input including its topographical and functional representation within the zones of the olivo-cerebellar system will be studied in cats and rabbits. 2) The descending projections of vertical and horizontal vestibular neurons to proximal neck movers will be determined in the cat. These specialized cervical projections are hypothesized to reflect the vestibular canal organization. 3) The structure-function relationship of vertical canal related second order vestibular neurons to compensatory and voluntary eye movements will be established in the cat. 4) The specialized horizontal eye movement pathways, consisting of the ascending tract of Deiters and abducens internuclear neurons will be investigated in a comparative approach utilizing rabbits, goldfish, and fish which are considered "living fossils". These experiments focus on the phylogenetic development of ocular frontalization and fovealization in vertebrates. 5) The reciprocal excitatory-inhibitory innervation of the vestibulo-oculomotor system will be ascertained in fish. This work emphasized phylogenetic continuity of the particular push-pull operational mode. Experimental techniques include acute and chronic animal preparations, three-dimensional visual and vestibular stimuli with extra-and intracellular recordings, extra- and intracellular horseradish peroxidase (HRP), 2-deoxyglucose, and eye movement recordings with a magnetic search coil system. The long term objectives of the proposal is to demonstrate that the central nervous system employs preferred coordinates in order to simplify calculation processes, when dealing with sensory-motor systems of high degrees of freedom. These preferred coordinates may be expressed in distinct intrinsic reference frame systems, that will be reflected by characteristic neuronal pathways.