A Pixel-Encoder Retinal Ganglion Cell with Spatially Offset Excitatory and Inhibitory Receptive Fields

The spike trains of retinal ganglion cells (RGCs) are the only source of visual information to the brain. Here, we genetically identify an RGC type in mice that functions as a pixel encoder and increases firing to light increments (Pix(ON)-RGC). Pix(ON)-RGCs have medium-sized dendritic arbors and non-canonical center-surround receptive fields. From their receptive field center, Pix(ON)-RGCs receive only excitatory input, which encodes contrast and spatial information linearly. From their receptive field surround, Pix(ON)-RGCs receive only inhibitory input, which is temporally matched to the excitatory center input. As a result, the firing rate of Pix(ON)-RGCs linearly encodes local image contrast. Spatially offset (i.e., truly lateral) inhibition of Pix(ON)-RGCs arises from spiking GABAergic amacrine cells. The receptive field organization of Pix(ON)-RGCs is independent of stimulus wavelength (i.e., achromatic). Pix(ON)-RGCs project predominantly to the dorsal lateral geniculate nucleus (dLGN) of the thalamus and likely contribute to visual perception.