The initial activity-independent formation of a topographic map in the retinotectal system has long been thought to rely on the matching of molecular cues expressed in gradients in the retina and the tectum. However, direct experimental evidence for the existence of such gradients has only emerged in the past two years. The new data has provoked the discussion of a new set of models in the experimental literature. Here, these models are subjected to a rigourous theoretical analysis.
Geoffrey J. Goodhill