Fig. 7. Simulations of the development of connections between a full-size retina and a full-size colliculus when the initial pattern of innervation is random and the desired polarity of the map is specified by initial weak gradients of ephrins over the colliculus. (A) The initial concentration C(x) of ephrinA at a distance x along the rostrocaudal axis of the colliculus is assumed to vary as C(x) = 0.6x + 0.5II where II is a random number between 0 and 1. Similarly, the initial concentration D(y) of ephrinB along the lateromedial axis is D(y) = 0.6y + 0.5II. (B) Control with random initial ephrin distributions.