How do rods and cones contribute to the receptive fields of retinal ganglion cells?

Rods and cones serve as the primary photoreceptors that initiate the visual signal, forming the foundation of the receptive field of a retinal ganglion cell. The receptive field is defined by the specific group of photoreceptors that connect to a single ganglion cell, typically organized into a concentric center-periphery structure.123

The contribution of these receptors to the ganglion cell's response is mediated by complex synaptic connections:

• Convergence: Because there are significantly more photoreceptors than optic nerve fibers, multiple rods and cones converge onto bipolar cells, which in turn connect to ganglion cells. Rods generally exhibit higher convergence than cones, contributing to the high sensitivity of the retina in low-light conditions.24
• Center-Periphery Organization: Photoreceptors in the center of the field typically excite the ganglion cell, while those in the surrounding periphery inhibit it (or vice versa). This arrangement, facilitated by horizontal cells and amacrine cells, allows the ganglion cell to act as a detector of local contrast, movement, and contours rather than simply responding to uniform light intensity.135
• Color Opponency: In many ganglion cells, the connections to different types of cones allow for color-opponent responses, where specific wavelengths (e.g., red vs. green) have opposing excitatory and inhibitory effects on the center and surround.6