SPATIAL COORDINATES OF VISUO-VESTIBULO-OCULAR REFLEXES

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Eye and head movements that occur in three-dimensional space are commonly described by the extrinsic orthoganal x,y,z axes (Cartesian) coordinate system. However, for weak coordinated motor commands, especially those resulting from multisensory integration, biological systems are likely to utilize intrinsic reference frames that are geometrically different from Cartesian systems. Our prior studies in the accessory optic system and cerebellum indicated that the coordinate axis for the orientation frames of the vestibulo-oculo motor and visual climbing fibers were geometrically closely related. The planes were three-dimensional, non-orthogonal, oblique and axially symmetric to the midline and in fact, these results suggested that the vestibular coordinate system may form the basic geometric architecture. Accordingly, experiments are proposed to test the coordinates of the geometric space leading to visual modulation of identified secord order vestibular neurons including a broader morphological study of neuronal network underlying vertical vestibulo-ocular reflexes. In addition, both the signals and patterning of extraocular motoneuron and muscle activity leading to compensatory eye movement in lateral- and frontal-eyed animals will be studied. Rabbits and cats, respectively, will be used to determine if the orientation planes of identified vestibular neurons are indeed similar in the two species. Vestibular stimulation will be provided by a three-dimensional turntable and visual stimulation by a three-axis planetarium projector producing a full field constant pattern. The neuronal network underlying the vertical vestibular ocular reflexes will be studied with intracellular HRP methods. Standard neurophysiological techniques and eye movement measurement will be employed. Data analysis will be accomplished by on- and off-line computer compilation. The immediate objective of the project is to describe exactly how the semi-circular canal sensory planes are related to the instrinsic framework for other sensory and motor coordinate systems. This goal will be achieved by studying how different classes of information coded in each individual coordinates interact with each other and, more specifically, how this relationship is visualized in respect to central neuronal connectivity. The long term objective of the proposal is to test the hypothesis that the intrinsic coordinate system may be common for all vertebrate species, cat, rabbit, goldfish.