The overall goal of the proposed research is to further our understanding of the role of the otolith organs in maintaining the direction of gaze. The vestibulo-ocular reflex maintains direction of gaze, preventing blurred vision during head movement by using semicircular canal and otolith signals to rotate the eyes in the direction opposite to head motion. The canal-ocular reflex has been widely studied, but little is known about the otolith-ocular reflex. Otoliths are stimulated by any finite body motion in any direction, and especially by gravity, vertical rotations, or brief linear motion. The proposed research will characterize the vision-stabilizing eye movements produced by otolith responses and explore the underlying neural mechanisms in three series of experiments in cats. The results will tell us more about gaze stability and general brain mechanisms of control. (1) Characterization of otolith input to vestibulo-ocular reflex in three dimensions: eye movements will be recorded during sinusoidal linear and rotational motion in 3-D and across a range of gravity orientations and frequencies. Rotational and linear ocular reflexes will be recorded in response to velocity step and multi-frequency stimuli to assess latency and predictive responses. An otolith ocular reflex stabilizes gaze during low frequency rotations; proposed research will show whether the otolith vestibulo-ocular reflex stabilizes gaze during all linear motions and during high frequency rotational motions with a linear component. (2) control and adaptation by otolith vestibulo-ocular reflex: After characterizing the separate rotational and linear vestibulo-ocular reflexes under (1), Combined rotational and linear stimuli will be presented using a rotator on a linear sled and rotations about axes at various distances from the head. The ocular reflex responses to combined stimuli are expected to stabilize gaze more accurately than the sum of those in response to individual rotational or linear motions that present sub-optimal stimuli. Adaptive capacity, signal gating, and simple discriminative learning of linear otolith ocular reflexes will be tested. (3) Neural mechanisms of otolith-ocular reflexes: Responses will be recorded from vestibular nuclear neurons with electrically identified inputs and outputs in alert cats during experimental situations described under (1) and (2), to identify classes of neurons participating in otolith ocular reflexes. Spike-triggered averaging will be used to identify target muscles influences by second-order vestibular neurons. Canal and otolith signals on vestibular neurons will be distinguished and studies done of the influences of nodular and floccular vestibulo- cerebellum on these signals during the experiments above in (1) & (2). the results will demonstrate neural mechanisms of otolith vestibulo- ocular reflexes and show how the cerebellum influences vestibular nuclei output, controls signals, or provides a teaching signal for brainstem neurons.
Showing the most recent 10 out of 42 publications
