The purpose of this research is to characterize how adaptation of the angular vestibulo-ocular (aVOR) reflex depends on head orientation with regard to gravity and to determine its neural basis. The horizontal, vertical and torsional component of the aVOR will be adaptively increased and decreased in cynomolgus monkey (Macaca fascicularis) with the head in different positions. Angular rotation that is in-phase or out-of-phase with the visual surround will be used to decrease or increase the gain of the aVOR, respectively. Data obtained before and after adaptation will be compared. Magnitude of adaptive changes in various head orientations will be studied after one of the aVOR components has been adapted in a particular head position. Functional dependence of context-specific gain changes will be determined for each aVOR component. We expect that the amount of gain change will be maximal with the head in the same position in which the aVOR was adapted, and that changes will decrease as the head is deviated from this position. Based on the results of this experiment, our previous aVOR model will be extended to account for context specific gain changes. The neuronal basis of the context specific adaptation will be studied. When these studies are completed, we will have characterized context specific adaptation for canal activation in any plane and will have provided insights into the neural basis for this adaptation. An understanding of the neural basis of the context specific adaptation with regard to gravity is of considerable scientific interest, because this type of knowledge could have important implications for understanding adjustments to visual-vestibular conflict in gravitational environments. We postulate that context specific adaptation is one of the basic properties of the aVOR that is critical for orientation in three-dimensional space in the presence of gravity. Therefore, understanding of this phenomenon will significantly advance our knowledge of how the canals and otolith interact to maintain gaze stability.
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