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Noise in V2 neurons of amblyopic monkeys



Conference Title

Society of Neuroscience Annual Meeting


Society of Neuroscience


Washington, D.C. / November 15-19, 2014

Publication Date / Copyright Date



Binocular imbalance early in life, due to strabismus (ocular misalignment) or anisometropia (monocular defocus), is known to result in binocular vision deficits and often amblyopia, a developmental vision disorder. Although amblyopic humans commonly exhibit a severe loss of acuity and contrast sensitivity, a broad range of far more complex spatial and temporal vision deficits have been reported in the literature. One of the major ideas to explain the source of reduced vision in amblyopia is the increased ‘neural noise’ in their visual brain. However, there has not been any neurophysiological study to directly address this issue. Therefore we recorded from V2 neurons in adult monkeys reared with monocular defocus between 3 weeks and 3 months of age and developed moderate ansiometropic amblyopia. We investigated the possible origin of increased internal noise in amblyopes by analyzing the variability of spiking (fano factors) and the noise correlation among multiple nearby V2 neurons of our amblyopic monkeys. Stimuli were drifting gratings (3.1 Hz) optimized for orientation, spatial frequency, and size for each neuron. The variance to mean ratio of spiking and noise correlation were calculated for low (20%) and high (80%) stimulus contrasts. We found that with low contrast stimuli the VMR was significantly elevated in V2 neurons driven by both the amblyopic and fellow eyes compared to that in normal monkeys. With high contrast gratings, there was no difference between amblyopic and normal V2 neurons. Similarly, noise correlation in amblyopic monkeys was significantly higher than that in normal monkeys only when we used low contrast gratings. Our results suggest that the noisy firing of individual neurons and the elevated noise correlation in V2 of amblyopic monkeys may affect signal processing down stream, which in turn may affect their visual performance tested with low contrast stimuli.



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