For evolution to work, neural circuits must have a scalable architecture
-- that is, these circuits must be designed in a way that permits them
to process more information by simply increasing the circuit size rather
that redesigning it. I will describe one of the design principles that
govern such scalable circuits in the vertebrate brain. I start with a
consideration of the retina. Retinal ganglion cells (RGCs) sample
information about the visual scene and encode this information for
transmission to the brain. Because RGCs tile the retina, each RGC
constitutes a "pixel". How large should this pixel be? Using a
theoretical approach, I give an answer to this question. These same
ideas can be extended to a give general design principle (supported by
experimental evidence) that applies to circuits throughout the
vertebrate brain.