(A) simulation study on the developmental mechanism of salt-and-pepper orientation map in rodents visual cortex

Abstract

In primary visual cortex (V1) of mammals, the neurons selectively respond to the specific features of visual stimuli, such as orientation and spatial frequency. The spatial distribution of orientation preference of each V1 neuron forms the orientation map. Interestingly, the structure of orientation maps differs across species. The orientation preference of each neuron varied smoothly across V1 in higher mammals, such as monkeys and cats. On the other hand, the orientation preferences varied discontinuously in rodents, in a structure called a salt-and-pepper map. However, what makes this structural difference of orientation maps between higher mammals and rodents remains unclear. Previously, a model study suggested that $moir \acute{e}$ interference pattern between ON and OFF retinal ganglion cell (RGC) mosaics could originate periodic orientation maps. Also, the model study suggested that the spatial periodicity on RGC mosaic by $moir \acute{e}$ interference determines the structure of orientation maps. However, our preliminary analysis suggests that the spatial periodicity on RGC mosaic, estimated from mouse RGC mosaic data, is not restricted to a specific range to generate a salt-and-pepper map. To address this issue, we herein propose that feedforward convergence structure between the retina and V1 is the crucial factor that determines the structure of orientation maps. To find the retina-V1 feedforward convergence structures that develop a salt-and-pepper map, we modulated two parameters. The first parameter was the size of sampling range in RGC mosaic, and the second was the sampling ratio within the convergence structure, which indicates how densely RGCs were sampled. This dissertation suggests that a salt-and-pepper map can be developed by large, sparse convergence structure in retina-V1 feedforward wiring, while a smooth map can be developed by small, dense convergence structure. Furthermore, this model study proposes a possibility that feedforward convergence structure may decide the structure of functional map observed in the mammalian cortex.