AXONAL PROCESSES AND NEURAL PLASTICITY - III - COMPETITION FOR DENDRITES

In previous work we ha-iie developed a computational framework for top ographic map formation and plasticity based oil axonal process sprouti ng and retraction, in which sprouting and retraction are governed by c ompetition for neurotrophic support. Here we show that such an approac h can account for certain aspects of the dendritic morphology of corti cal maps. In particular, we model the development of ocular dominance columns in the primary visual cortex and show that cortical cells near to column boundaries prefer to elaborate dendritic fields which avoid crossing the boundaries. This emerges as different functional inputs are spatially? separated. We predict that afferent segregation occurs before or simultaneously with, but not after; the emergence of dendrit ic bias. We predict that animals reared with complete but asynchronous stimulation of the optic nerves do not develop a dendritic bias. ;We suggest that the emergence of a dendritic bias might provide a partial account for the critical period for a response to monocular deprivati on. In particular, we predict that animals reared with asynchronous op tic nerve stimulation might exhibit an extended critical period. Our r esults also indicate that the number of synapses supported by cortical cells depends on the intra-ocular image correlations used in our simu lations. This suggests that inter-ocular image correlations, and thus strabismic rearing of kittens, may also affect the innervation density .