Axonal pathfinding at the optic chiasm and at decision regions: control of growth cone motility, guidance, and cellular contacts

Studies of fiber guidance in invertebrates and at decision regions in vertebrates, show that three different sets of processes intervene. The first, is complex interactions of growing fibers with cells, often neuronal, that exist at strategic locations, at special borders or at decision points. The second is a modulation of growth cone motility, which manifests itself by a stop-start pattern of advance. The third, is response of growth cones to guidance cues, which are presumed to be distributed in graded or abrupt spatial distributions. In this paper, I will review the process of retinal fiber decussation from this point of view, with the aim of demonstrating how each of these processes contributes to fiber growth in this and other decision regions.