Parallel processing in retinal ganglion cells: How integration of space-time patterns of excitation and inhibition form the spiking output

Our goal was to understand how patterns of excitation and inhibition, interacting across arrays of ganglion cells in space and time, generate the spiking output pattern for each ganglion cell type. We presented the retina with a 1-s flashed square, 600 mu m on a side, and measured patterns of excitation and inhibition over an 1,800-mu m-wide region encompassing many ganglion cells. Excitatory patterns of ON ganglion cells resembled rectified versions of the voltage patterns of ON bipolar cells. Inhibitory patterns in ON ganglion cells resembled the rectified versions of voltage patterns of OFF bipolar cells. OFF ganglion cells received OFF excitation and ON inhibition. Many ganglion cells also received an additional wide field transient inhibition derived from the activity of both ON and OFF bipolar cells. Ganglion cell spiking was suppressed in those space- time regions dominated by inhibition. We classified each ganglion cell type by correlating its space- time patterns with its dendritic morphology. These studies suggest the bipolar and amacrine cell circuitry underlying the interplay between ON and OFF signals that generate spiking patterns in ganglion cells. They reveal a surprising synergistic interaction between excitation and inhibition in most ganglion cells.