Is binocular competition essential for layer formation in the lateral geniculate nucleus?

In this paper we examine mechanisms that could explain how layers form within the lateral geniculate nucleus (LGN). Analysis of normal LGN development and development following experimental or genetic perturbation, together, suggest that binocular competitive interactions alone cannot account for either the segregation of retinogeniculate axons or subsequent formation of cell layers. Instead, it appears more likely that initial sorting of axons results from an activity-dependent interaction between populations of axons with different identities and differential affinities for postsynaptic LGN targets. Competitive interactions, however, may aid in sorting axons of like type or in refining topography. We also propose that the subsequent steps in LGN layer formation, such as the formation of interlaminar spaces, depend upon a sequence of interactions between retinal axons, extraretinal axons and outgrowth of developing dendrites of LGN cells.