Layout and Function of the Intracortical Connections within Layer 4 of Cat Area 17

A patch of layer 4 of cat area 17 has been modeled. The developmental network model is based on the modular structure of the neocortex. Connections between the orientation minicolumns, building the network model, are developed during exposure to visual input. The network model captures some of the known properties of the layer 4 of cat area 17. Local connections are dense, whereas distal connections are sparse. Both local and distal inhibition is mediated by inhibitory simple cells, which target excitatory cells that are located in their close surroundings and have opposite absolute and relative spatial phase. Excitatory local connections seem to be biased towards the iso-orientation domain. However, there is a strong crosstalk between all orientation domains made by the excitatory long-range horizontal connections. Furthermore, the excitatory long-range horizontal connections are mildly elongated along the orientation axis. We hypothesize that this network layout can give a simple explanation to the psychophysical experiments demonstrating response facilitation as a result of elongation of a Gabor patch along the orientation axis.