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Figure 7 Evidence for high degree of convergence from TL inputs to PyrNs. (A) Maximum projection image of fluorescence in a 7 dpf Tg(HuC:lynTagRFP-t) larva. (B) Maximum projection of boxed subregion in (A) rotated −40° about the Y-axis, an orientation orthogonal to the tectal layers used for retinotopic area measurements. Maximum projection of equivalent subregions in a 7 dpf Tg(hspGGFF23C,uas:egfp,isl2b:TagRFP) larva rotated −40° about the Y-axis. Yellow polygon drawn to assist in comparison of area differences between the three images. (C) Schematic at left summarizes tectal inputs from TL-recipient SM layer (cyan), retinorecipient layers (red), and total tectal neuropil area. Schematic at right summarizes area measurements for these different neuropil layers. (D) Skeletonized tracings and average retinotopic areas for TL axons, RGC axons, and PyrN neurite subregions. (E) Implications of size disparity between TL axon arbors and retinal axon arbors in tectum. TL axon arbor areas are depicted as cyan circles and RGC axon arbor areas are red ovals. Due to the large size of TL arbors, a PyrN dendrite at the center of SM has the potential to contact all TL inputs. Conversely, the small relative size of RGC axons innervating SFGS means that a PyrN dendrite at the center of SFGS has the potential to contact only a small fraction of retinal inputs to SFGS. Due to the small size of both pre- and post-synaptic elements this remains true even as the number of RGC inputs increases. Scale bar: 200 μm in (A) and 100 μm in (B).