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H Bi, B Zhang, T Mori, E Sakai, N Noska, RS Harwerth, Y Chino, EL Smith; Effects of Early Strabismus On The Development of Binocular Response Properties of Neurons In Visual Area 2 (v2) Of Rhesus Monkeys . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4776.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Although alterations of the binocular response properties of neurons in the primary visual cortex (V1) of monkeys reared with experimentally imposed strabismus have been well characterized, very little is known about the effects of early abnormal visual experience on the development of extrastriate neurons. In this study, we investigated the binocular response properties of V2 neurons in monkeys reared with early surgical strabismus. Methods:A small convergent misalignment was surgically induced in five infant monkeys at 4 weeks of age. Behavioral testing to measure their monocular and binocular visual capacities with respect to amblyopia, stereodeficiencies and residual strabismus were conducted between 2 and 4 years of age. Upon completion of the behavioral testing, extracellular single-unit recording experiments were conducted under anesthesia and paralysis. The binocular response properties of V2 neurons were quantitatively assessed. The data obtained in V2 were compared to those in V1 of the same monkeys. Results:The ocular dominance tests revealed that a relative reduction of binocularly balanced units in V1 was significantly greater than that in V2. However, the sensitivity of V2 units to relative interocular spatial phase disparity was significantly reduced in both V1 and V2. There was an increase in the proportion of units exhibiting interocular suppression in V2 relative to V1 in strabismic monkeys. The observed binocular suppression in V2 units of strabismic monkeys was more pronounced for higher spatial frequency gratings. This spatial frequency dependent increase in the prevalence of binocularly suppressive units was much less clear in V1. Conclusion:Alterations in how binocular signals are combined in V2 neurons of strabismic monkeys are generally more extensive and more complex than those in V1. The results suggest that these deficits in V2 are not a mere reflection of anomalies in V1 but may include a consequence of active competitive processes in V2.
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