Current Biology
Volume 29, Issue 3, 4 February 2019, Pages 381-391.e4
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Article
Binocular Modulation of Monocular V1 Neurons

https://doi.org/10.1016/j.cub.2018.12.004Get rights and content
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Highlights

  • Monocular neurons in primate V1 layer 4C encode binocular inputs

  • Firing rates of most monocular V1 neurons are suppressed under binocular viewing

  • A neuron’s ocularity and its binocular modulation are linearly related

Summary

In humans and other primates, sensory signals from each eye remain separated until they arrive in the primary visual cortex (V1), but their exact meeting point is unknown. In V1, some neurons respond to stimulation of only one eye (monocular neurons), while most neurons respond to stimulation of either eye (binocular neurons). The main input layers of V1 contain most of the monocular neurons while binocular neurons dominate the layers above and below. This observation has given rise to the idea that the two eyes’ signals remain separate until they converge outside V1’s input layers. Here, we show that, despite responding to only one eye, monocular neurons in all layers, including the input layers, of V1 discriminate between stimulation of their driving eye alone and stimulation of both eyes. Some monocular V1 neurons’ responses were significantly enhanced, or facilitated, when both eyes were stimulated. Binocular facilitation within V1’s input layers tended to occur at the onset of the visual response, which could be explained by converging thalamocortical inputs. However, most V1 monocular neurons were significantly reduced, or suppressed, to binocular stimulation. In contrast to facilitation, binocular suppression occurred several milliseconds following the onset of the visual response, suggesting that the bulk of binocular modulation involves cortical inhibition. These findings, combined, suggest that binocular signals arise at an earlier processing stage than previously appreciated, as even so-called monocular neurons in V1’s input layers encode what is shown to both eyes.

Keywords

binocular vision
monocular neurons
binocular combination
binocular summation
binocular integration

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These authors contributed equally

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