What do species differences in cortical map organization reveal about the evolution of cortical circuitry?

The neocortex exhibits striking differences in spatial organization across mammals, from randomly arranged maps in rodents to smoothly varying topological maps in primates. This chapter explores what these differences reveal about the evolutionary pressures shaping cortical circuitry. We show that topological maps emerge through selforganization driven by short-range excitation, long-range inhibition, Hebbian learning, and the correlational structure of inputs. However, these ingredients alone do not explain why some species lack such maps. We propose that distinct wiring regimes have evolved in response to differences in integration demands: in species with large pools of correlated neurons, sparse long-range connectivity combined with dense local excitation minimizes wiring cost and gives rise to topological maps as a by-product. Conversely, in species with smaller correlation pools, uniformly distributed lateral connectivity is more efficient, precluding map formation. Thus, cortical maps may reflect emergent signatures of wiring optimization, not direct evolutionary targets, shaped by how correlated inputs are projected onto cortical space.