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Kacie Dougherty, Michele A Cox, Jacob A Westerberg, Alexander Maier; Binocular Modulation of Monocular Neurons in the Primary Visual Pathway. Journal of Vision 2019;19(10):130c. doi: https://doi.org/10.1167/19.10.130c.
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© ARVO (1962-2015); The Authors (2016-present)
Our brains reliably transform the patterns of light on the two retinae into a singular view. Retinal projections from each eye target mutually exclusive groups of neurons in the lateral geniculate nucleus (LGN) of the thalamus. Congruent with this pattern of innervation, almost all LGN neurons respond to one eye and not the other (monocular neurons). In V1, some neurons, especially in the primary LGN input layer, respond to only one eye as well. However, most V1 neurons respond to either eye (binocular neurons), though stimulation of one eye (the dominant eye of the neuron) often leads to a greater response than stimulation of the other. These findings suggest that the two eyes’ signals are combined into a binocular response before they leave V1. However, we do not know exactly where this happens as even monocular neurons might be sensitive to both eyes. For example, monocular neurons could significantly alter, or modulate, their responses during binocular stimulation compared to stimulation of their dominant eye alone. To test for this possibility, we used linear multicontact electrode arrays to record LGN and V1 spiking responses to visual stimuli presented to one or both eyes at varying contrast levels. While the majority of LGN neurons did not modulate during binocular stimulation, approximately one-fifth of LGN units showed a significant difference between monocular and binocular stimulation, consistent with earlier reports in anaesthetized animals. In stark contrast, most monocular V1 neurons, including those in the primary LGN input layer, significantly modulated their responses during binocular viewing. Most of this binocular modulation occurred several milliseconds following the onset of the visual response, suggesting that the bulk of binocular modulation involves intracortical processing.
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