Figure 5.
A standard pattern is generated by a model that uses densities of each cell type and typical patterns of divergence and convergence to capture the unit of connectivity across the three-tiered mosaic, a tile that repeats across the retina to generate the complete connectivity. *A*, Each S cone diverges to four S-cone ON bipolar cells, distributing its ∼30 ribbon synapses in the ratio 3:6:9:12, represented by 1, 2, 3, and 4 blue bonds. Two S cones converge on each bipolar cell. The S-cone bonds, in four configurations (a–d), are arranged so that single blue bonds are opposite quadruple blue bonds, and double blue bonds are opposite triple blue bonds, permitting each S-cone ON bipolar cell to collect five blue bonds, representing 15 ribbon synapses. Each S-cone ON bipolar cell diverges to two BY ganglion cells, distributing 14 ribbon synapses (single green bond) to one ganglion cell and 28 (double green bond) to the other. *B*, From the patterns of divergence and convergence at each level, plus the cell densities at each level (Fig. 3), we derive a unit of connectivity (large, gray diamond). It includes 16 ganglion cells in pairs within eight smaller diamonds. The standard pattern emerges: half of the ganglion cells are dominated by one S cone, half by more than one S cone, and each S cone dominates a single BY ganglion cell but contributes to several others. *C*, The large gray diamond in *B*, containing eight small diamonds (1–8), represents the unit of connectivity that repeats in larger arrays. A complete set thus includes the eight pairs of BY ganglion cells, the synaptic weights of which are shown in *B*, and eight S cones, one (the north one, for example) from each of the eight small diamonds. *D*, The model (*B*) establishes that each S cone diverges to six BY ganglion cells, dominating one of the six and contributing to the other five.