Synaptic Organization of the Primate Retina: Toward a Human Foveal Connectome.

The great diversity of retinal cell types across mammalian species, including humans, is well recognized. Recent transcriptomic profiling has not only confirmed this diversity but also identified homologous cell types across species, revealing molecular conservation of cell type identity. Yet retinal circuits are functionally specialized for distinct visual behaviors across species, raising a key question: If cell types are conserved, then what drives this functional specialization? The answer requires mapping the precise synaptic connections among all cell types-information that has long been difficult to acquire. Here we review, specifically for primates, how artificial intelligence-powered connectomics directly addresses this fundamental question by creating complete retinal connectomes that capture the synaptic connections formed by all cell types within a retinal volume. Recent data from a human foveal connectome suggest that while retinal cell types may be molecularly conserved across human and nonhuman primates, differences in synaptic connectivity drive species-specific functional specialization. Thus, synaptic connectivity, not just cell type identity, drives evolutionary adaptation.