Research overview: the rod bipolar and AII amacrine night-vision circuit

Night vision depends not only on rods but on a dedicated downstream circuit that carries their signals into the rest of the retina. This survey reviews the rod bipolar to AII amacrine cell pathway, a specialized route that feeds dim-light signals into the cone circuitry for transmission to the brain. The cat retina has been an influential model for working out this circuitry, which allows a single photon-driven rod response to be amplified and routed efficiently in scotopic conditions. The overview connects the anatomy of these interneurons to the high sensitivity and pooling that characterize feline night vision. Because the rod pathway converges strongly before reaching ganglion cells, it boosts detection at the cost of resolution, mirroring the broader sensitivity-acuity tradeoff. This circuit illustrates how the cat's dim-light prowess is built into retinal wiring, not just photoreceptor counts.