A robust and versatile capability for adaptive control of the vestibuloocular reflex (VOR) is essential for an organism to maintain optimal vision throughout life. Changes with development, aging, disease and trauma, demand mechanisms to detect and correct errors in performance. An understanding of such adaptive mechanisms bears on a fundamental problem in neuroscience -- motor learning -- and is also essential for accurate clinical diagnosis and the design of physical therapy programs. The long-term goal of this research is to understand how humans adapt to vestibular disorders, with the practical aim of developing better physical therapy programs for patients with vestibular disorders. The specific objective of this project is to learn more about the mechanisms underlying short-term -- minutes to hours -- VOR adaptation in normal humans. The emphasis is upon adaptive control of 1) otolith-ocular reflexes, 2) the phase of the canal and otolith-ocular reflexes, and 3) the torsional VOR. The error signals and contextual cues that lead to the expression of adapted responses will be evaluated. The relationship of adaptation of the VOR to the function of the ocular motor gaze-holding neural integrator, and to predictive pursuit mechanisms will also be investigated. Relatively little is known about these aspects of vestibular physiology, and each potentially bears on important issues related to vestibular adaptation, the error signals that drive it, and how adaptation can be promoted in patients. Eye movements will be measured using the magnetic field search coil technique. Otolith-ocular reflexes will be elicited in response to changes in the orientation of the head with respect to gravity (ocular counterroll), during eccentric rotation, which combines angular and linear acceleration, and in response to translation on a linear sled. Adaptation will be elicited using a visual-vestibular conflict paradigm in which the VOR is made to seem inappropriate by rotating or translating the visual scene (an optokinetic drum or a projected visual scene relative to the motion (rotation or translation) of the head). The results of such experiments will have important theoretical implications for basic vestibular physiology (and lend themselves to experimental neurophysiological study and mathematical modeling) as well as potential practical applications to clinical neurootology.
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