POSSIBLE ROLES OF SPONTANEOUS WAVES AND DENDRITIC GROWTH FOR RETINAL

Several models of cortical development postulate that a Hebbian proces s fed by spontaneous activity amplifies orientation biases occurring r andomly in early wiring, to form orientation selectivity. These models are not applicable to the development of retinal orientation selectiv ity, since they neglect the polarization of the retina's poorly branch ed early dendritic trees and the wavelike organization of the retina's early noise. There is now evidence that dendritic polarization and sp ontaneous waves are key in the development of retinal receptive fields . When models of cortical development are modified to take these facto rs into account, one obtains a model of retinal development in which e arly dendritic polarization is the seed of orientation selectivity, wh ile the spatial extent of spontaneous waves controls the spatial profi le of receptive fields and their tendency to be isotropic.