Functional Synaptic Organization of Ocular Dominance within the Dendritic Field of Layer 2/3 Neurons in Ferret Visual Cortex

Clara Tepohl1, Benjamin Scholl1, David Fitzpatrick1


Neurons in primary visual cortex (V1) exhibit binocular responses that differ in ocular dominance--the relative strength of the inputs from the two eyes. How the ocular dominance properties of individual neurons are generated from the pattern of excitatory inputs that synapse within their dendritic field remains unknown. To address this question, we used in vivo two-photon calcium imaging of dendritic spines, recipients of excitatory inputs, on individual layer 2/3 neurons in ferret V1. To characterize functional properties, we measured orientation tuning and ocular dominance of spines and corresponding somatic output.

Synaptic inputs onto individual cells varied broadly in ocular dominance, rather than strictly matching the eye preference of the soma. This led us to explore whether the spatial arrangement of synaptic inputs within the dendritic field could contributing to somatic ocular dominance. We found no differences in the distribution of ocular dominance values between apical and basal dendrites. However, on several branches, synaptic inputs were more similar or dissimilar to each other in terms of ocular dominance and orientation preference than would be expected by chance, consistent with a branch-level organization of these functional properties. In addition, we observed a non-random fine-scale spatial organization of ocular dominance within individual dendritic branches. Taken together, these results suggest that multi-scale spatial arrangements of synaptic inputs within the dendritic field may contribute to the functional integration of eye-specific synaptic inputs.