Subcortical Foundations of Binocular Vision: Circuits and Computation from Retina to Cortex and Back.

Binocular integration is a well-established feature of neuronal processing in the primary visual cortex, where such integration is thought to first emerge. However, accumulating evidence demonstrates that subcortical retinorecipient nuclei possess sophisticated binocular processing capabilities, with important implications for cortical function, visual behavior, and non-imaging-forming physiology. This review synthesizes our current understanding of the circuit origins and functional relevance of binocular integration and modulation in the dorsal lateral geniculate nucleus, superior colliculus, and other subcortical targets. We describe how the definition of binocularity has evolved beyond simple ocular dominance to encompass diverse modes of neuronal modulation, including facilitation, summation, suppression, and emergent responses. We highlight the prevalence of multiple wiring motifs subserving binocular convergence, including direct retinal inputs, lateral circuits via local interneurons, feedback from cortical or subcortical sources, and indirect relays through intra- or interhemispheric connections. Recent anatomical and functional studies reveal substantial binocular integration despite apparent eye-specific input segregation, with region- and species-specific differences reflecting distinct ethological demands. Finally, elucidation of a critical role for subcortical binocular processing in prey capture and threat responses is expanding our cortex-centric view and revealing new complexity in the regional distribution of visual computations essential for survival behaviors.