A Model of Monocular Cell Development by Competition for Trophic Factor

Abstract

Recent experimental evidence has shown that application of certain neurotrophic factors (NTs) to the developing primary visual cortex prevents the development of ocular dominance (OD) columns. One interpretation of this result is that afferents from the lateral geniculate nucleus (LGN) compete for postsynaptic trophic factor in an activity dependent manner. Application of excess trophic factor eliminates this competition, thereby preventing monocular cell development. We present a model of monocular cell development, incorporating Hebb-like synaptic modification and activity-driven competition for NT, which accounts for the following results: 1) monocular cells form normally when available NT is below a critical amount, 2) monocular cells form in the presence of positive inter-eye correlations, while being entirely self-normalizing in that no normalization of synaptic strengths is necessary to enforce the competition, and 3) monocular cells are prevented in a local neighborhood in which excess NT has been added. The model integrates several disparate neurobiological findings into a cohesive framework, and makes predictions concerning the quantitative dependence of monocular cell development on trophic factor availability.