Must pinwheels move during visual development ?

Abstract

The pinwheel-like arrangement of iso-orientation domains around orientation centers is a ubiquitous structural element of orientation preference maps in primary visual cortex. Here we investigate how activity-dependent mechanisms constrain the way in which orientation centers can form during visual development. We consider the dynamics of a large class of models for the activity-dependent self-organization of orientation preference maps. We prove for this class of models that the density of orientation centers which proliferate as orientation selectivity arises from an unselective state exhibits a universal lower bound. At least π/Λ² pinwheels must form initially, where d is the characteristic wavelength of iso-orientation domains. Due to topological constraints the density of orientation centers can only change by discrete creation and annihilation events. Consequently densities lower than π/Λ² must develop through an initial overproduction and subsequent annihilation of pinwheels. Monitoring the density of orientation centers during development therefore offers a powerful novel approach to test whether orientation preference arises by activity-dependent mechanisms or is genetically predetermined.