Functional convergence of on-off direction-selective ganglion cells in the visual thalamus

In the mouse visual system, multiple types of retinal ganglion cells (RGCs) each encode distinct features of the visual space. A clear understanding of how this information is parsed in their downstream target, the dorsal lateral geniculate nucleus (dLGN), remains elusive. Here, we characterized retinogeniculate connectivity in Cart-IRES2-Cre-D and BD-CreER2 mice, which labels subsets of on-off direction-selective ganglion cells (ooDSGCs) tuned to the vertical directions and to only ventral motion, respectively. Our immunohistochemical, electrophysiological, and optogenetic experiments reveal that only a small fraction (<15%) of thalamocortical (TC) neurons in the dLGN receives primary retinal drive from these subtypes of ooDSGCs. The majority of the functionally identifiable ooDSGC inputs in the dLGN are weak and converge together with inputs from other RGC types. Yet our modeling indicates that this mixing is not random: BD-CreER(+) ooDSGC inputs converge less frequently with ooDSGCs tuned to the opposite direction than with non-CART-Cre(+) RGC types. Taken together, these results indicate that convergence of distinct information lines in dLGN follows specific rules of organization.

Automated summary

In this study, the researchers investigated the connectivity between retinal ganglion cells (RGCs) and the dorsal lateral geniculate nucleus (dLGN) in the mouse visual system. They found that only a small fraction of thalamocortical neurons in the dLGN received primary retinal input from specific subtypes of RGCs. The majority of the functionally identifiable inputs from these RGC subtypes were weak and converged with inputs from other RGC types.