A binocular synaptic network supports interocular response alignment in visual cortical neurons

In visual cortex, signals from the two eyes merge to form a coherent binocular representation. Here we investigate the synaptic interactions underlying the binocular representation of stimulus orientation in ferret visual cortex with in vivo calcium imaging of layer 2/3 neurons and their dendritic spines. Individual neurons with aligned somatic responses received a mixture of monocular and binocular synaptic inputs. Surprisingly, monocular pathways alone could not account for somatic alignment because ipsilateral monocular inputs poorly matched somatic preference. Binocular inputs exhibited different degrees of interocular alignment, and those with a high degree of alignment (congruent) had greater selectivity and somatic specificity. While congruent inputs were similar to others in measures of strength, simulations show that the number of active congruent inputs predicts aligned somatic output. Our study suggests that coherent binocular responses derive from connectivity biases that support functional amplification of aligned signals within a heterogeneous binocular intracortical network. [Display omitted] •Layer 2/3 neurons in visual cortex receive monocular and binocular synaptic inputs•Monocular inputs alone cannot account for somatic binocular alignment•Binocular congruent inputs exhibit functional properties ideally suited for alignment•Dominant influence of binocular congruent inputs derives from strength in numbers Scholl, Tepohl, et al. investigate how signals from the two eyes are combined within synaptic populations of individual neurons to shape a coherent representation. Rather than a convergence of monocular streams, they find that intracortical binocular networks are key to shaping alignment in cortical layer 2/3.