Neural organization of eye movements in depth

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DESCRIPTION (provided by applicant): Disconjugate oculomotor responses, where the two eyes rotate by different amounts, are often needed. Hering's law of equal innervation states that there are two groups of oculomotor commands. Conjugate commands rotate the eyes in the same amount in the same direction similarly to a yoked pair. Vergence commands control the angle between the eyes by rotating the eyes in same amount in the opposite direction. Any disconjugate eye rotation can be obtained by appropriate conjugate and vergence commands. Recent evidence shows that some disconjugate responses may be driven by independent left- and right-eye asymmetric commands, perhaps directly reaching the motor neurons outside the vergence pathway. Are these putative monocular signals functionally significant? We will address this question by estimating the percentage of disconjugate command encoded by the vergence system directly at the neuronal level. If Hering's law is correct, the vergence system must account for the entire disconjugate response, independently of the type of stimulus or the oculomotor system in which it was generated. These estimates will be done during: 1) voluntary transfers of gaze in depth between stationary targets; 2) voluntary smooth tracking of small objects moving in depth; 3) ultra-short latency reflexive visual stabilization responses; and 4) linear vestibulo-ocular responses. Neural targets for the single-unit recordings will be the vergence-related cells in midbrain. Binocular horizontal, vertical, and torsional eye movements will be recorded together with the neural activity of these cells. High-field anatomical and functional MRI will help localize these areas. Visual function is severely degraded by double vision. At least 4% of the US population is affected by long- term deficits in binocular alignment, such as strabismus and amblyopia. The understanding of how disconjugate commands are generated and delivered to the extraocular muscles is of critical importance in developing a correct clinical management of oculomotor disorders affecting binocular alignment, both as diagnosis of the source of the oculomotor deficit and the selection of the proper surgical or optical intervention. Knowledge of the neural substrate of these mechanisms will be a crucial tool in the understanding of the oculomotor adaptive processes that help a patient recalibrate his/her eye movement commands to regain, or at least partially improve, binocularity, which are poorly understood.