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E Sakai, T Mori, B Zhang, H Bi, N Noska, RS Harwert, Y Chino, EL Smith III; Directional Bias of Neurons In Visual Area 2 (v2) of Monkeys Reared With Early Strabismus . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4775.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Humans and monkeys with early strabismus are known to exhibit monocular naso-temporal asymmetries in pursuit eye movements and visual tracking, similar to those found in normal neonates. To gain insight into the neural basis for these oculomotor asymmetries, we investigated the directional bias of neurons in cortical areas V1 and V2 of strabismic monkeys. Methods:Unilateral convergent misalignment was surgically induced in five infant monkeys at 4 weeks of age. The monkeys were reared in a normally lighted visual environment and behavioral testing to measure their monocular and binocular capacities were conducted between 2 and 4 years of age. Upon completion of the behavioral testing, we conducted extracellular single-unit recording experiments under anesthesia and paralysis in which we assessed the directional bias of individual V2 neurons (N=323) using a vector summation method. Results:We did not find an overabundance of V2 units preferring the temporal to nasal direction of stimulus drift. Instead, we found that the overall directional bias of V2 units was significantly reduced in strabismic monkeys compared to that in normal monkeys. These reductions were slightly larger for those units dominated by the behaviorally amblyopic eye. Comparable deficits in directional bias were also found for V1 neurons in these monkeys. Conclusion:Our results suggest that the oculomotor asymmetries in strabismic monkeys are not due to asymmetries in the directional properties of V1 or V2 neurons, but rather due to very impoverished cortical control over the brain stem nuclei that initiate eye movements.
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