Vergence eye movements are required to foveate an object of interest located either behind or in front of the current fixation point. In addition, appropriate ocular accommodation is required to bring this object into focus. Problems with these eye movements may result in insufficient or excessive vergence and ocular accommodation. Furthermore, the inability to converge or diverge the eyes appropriately may result in strabismus, which can often lead to amblyopia in children. Unfortunately, very little is currently known about the areas of the brain involved in controlling these eye movements or about the sensorimotor transformations that are required for their neural control. Therefore, the long-term objectives of the proposed experiments are to obtain a better understanding of the neural circuits and sensorimotor transformations underlying these eye movements. Recently, a region of the prearcuate cortex immediately anterior to the frontal eye fields has been reported by us to contain neurons related to vergence and accommodation (near-response and far-response neurons) and neurons related to the visual cues that drive these eye movements such as disparity and blur. Identification of this cortical area is a significant step forward and, this application proposes to more closely examine its role in controlling vergence and accommodation. Specifically, experiments will examine the responses of neurons in this region of prearcuate cortex to the major visual cues for vergence and accommodation such as disparity and blur, as well as their responses to specific motion-in-depth cues. The visual responses of these neurons to static and motion-in-depth cyclopean targets will also be examined. The motor responses of these neurons will be studied during those vergence and accommodative eye movements required to look between stationary targets at different depths, and during those that are required to track targets moving in depth. To examine the characteristic of the vergence and accommodation signals sent to pontine regions by these prearcuate neurons, they will be antidromically activated from the nucleus reticularis tegmenti pontis, which possesses a well-defined vergence and accommodation region. To examine the functional role of this prearcuate area in vergence and accommodative eye movements, it will be ablated both unilaterally and bilaterally. Based on smooth pursuit and saccadic deficits following frontal eye field lesions, deficits are predicted in the ability to track targets moving in depth and in the ability to perform movements to remembered targets at different depths, and potential deficits in these abilities will be specifically investigated.
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