Mechanisms for stable and robust development of orientation maps and receptive fields

Development of orientation maps in ferret and cat primary visual cortex (V1) has been shown to be stable, in that the earliest measurable maps are similar in form to the eventual adult map, robust, in that similar maps develop in both dark rearing and in a variety of normal visual environments, and yet adaptive, in that the final map pattern reflects the statistics of the specific visual environment. How can these three properties be reconciled? Using a mechanistic model of the development of neural connectivity in V1, we show how including two lowlevel mechanisms originally motivated from single-neuron results makes development stable, robust, and adaptive. Specifically, contrast gain control in the retinal ganglion cells and the LGN reduces variation in the presynaptic drive due to differences in input patterns, while homeostatic plasticity of V1 neuron excitability reduces the postsynaptic variability in firing rates. Together these two mechanisms lead to maps that develop stably and robustly, yet adapt to the visual environment. The modelling results suggest that topographic map stability is a natural outcome of low-level processes of adaptation and normalization. The resulting model is also a more robust yet simpler and more realistic model of map development than previous models, and is thus a good starting point for future studies of cortical map development.