A model for self-organization of receptive fields and orientation-selective columns in the striate cortex.

In area 17 of the cat visual cortex, simple cells form a hypercolumn in which the optimum orientation from one column to the next gradually changes, composing a complete set of orientation-selective columns (orientation column). This article proposes a model for the development of the bar-shape receptive field of a simple cell and the self-organization of orientation columns. The receptive field of an immature cell in area 17 is assumed to be composed of a circular center and surrounding regions whose synaptic modification rules are different. The synaptic modifications also differ depending on whether the response of a cell is locally maximal or not. The modification of the efficacy of both excitatory and inhibitory synapses is determined according to the combination of activities of the visual cortical cell and the lateral geniculate neuron. The simulation of this model shows the development of the bar-shape receptive field and the self-organization of orientation columns of more than one cycle from 0 degrees to 180 degrees. The abnormal presentations of visual stimuli to this model result in the abnormal development of the orientation column. These simulation results are in good agreement with reported experimental results. Possible neural circuits to achieve this model are proposed. The neural circuits for the synaptic modification are built on the assumption that cortical cells release molecules to modify synaptic efficacies. The neural circuits for the detection of the maximally responding cell are composed of two kinds of inhibitory interneurons. The bar-shape receptive field is assumed to be a consequence of the topographic projection of visual afferents, radial branching of dendrites of a simple cell, and the existence of an inhibitory interneuron.