Limited transmission of mixed convergent signals at the mouse retinogeniculate synapse.

There are two broad modes of information transfer in the brain: the labeled line model, where neurons relay inputs they receive, and the mixed tuning model, where neurons transform different inputs. In the visual pathway, information transfer between retinal ganglion cells (RGCs) and dorsal lateral geniculate nucleus (dLGN) neurons is viewed as a labeled line. However, recent work in mice demonstrated that different RGC types, encoding distinct visual features, converge onto a dLGN neuron, raising the question of how the dLGN transforms visual information. Using optogenetics, we activated distinct RGC populations and measured dLGN neuron spiking in vivo. We found that visual response properties of strongly driven dLGN neurons largely match properties of the activated RGC population. While in vitro dual-opsin experiments demonstrate that strong functional convergence from distinct RGC types does occur at modest frequencies, our data largely support a labeled line model of retinogeniculate information transfer in mice.