Abstract
Purpose :
The primate retina contains ~20 anatomically identified retinal ganglion cell (RGC) types and >10 polyaxonal amacrine cell (PAC) types. However, only 7 RGC types and 1 PAC type have been studied functionally in detail. Our goal is to understand the diversity of visual processing in the RGC and PAC types of the macaque and human retina.
Methods :
Large-scale multi-electrode recordings were performed from the peripheral retina. The spike-triggered average of each cell was calculated from responses to flickering checkerboards and used to summarize its spatial, temporal and chromatic properties. Cell types were identified by clustering their functional properties. Substantial errors due to spike sorting were ruled out by stereotypical properties of cells across the electrode array, refractory periods, spatiotemporal structure of electrical footprints, and mosaic organization of receptive fields (RFs) within each type.
Results :
In every recording, the well-known ON & OFF parasol, ON & OFF midget, ON & OFF smooth monostratified, and small bistratified RGCs, and A1 PACs, were identified. In 12 macaque retina recordings, at least 15 new RGC and 12 new PAC types with distinct RF properties were identified (Fig. 1A). Each new cell type was observed in several retinas. Most of the novel cell types exhibited one or more unusual properties: 1) inhomogeneous spatial RFs composed of multiple spots or branches; 2) spatially segregated ON and OFF inputs, driven by L/M cones or S cones, not in a center-surround arrangement (Fig. 1B); and 3) sparse spiking in response to checkerboards and naturalistic movies. In 4 human retina recordings, ~20 putative homologs of macaque RGC and PAC types were identified (Fig. 1B). One human PAC type exhibited double the spatial density of its macaque homolog, and one had no obvious homolog.
Conclusions :
Most novel RGC and PAC types in the primate retina exhibited unusual spatial and spectral RF properties and firing patterns, suggesting specific functions in visual processing. While most human cell types appear to have macaque homologs, a few cells and properties may be unique to the human retina.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.