Journal of Neuroscience in press AN EMERGENT MODEL OF ORIENTATION SELECTIVITY IN CAT VISUAL CORTICAL SIMPLE CELLS

It is well known that visual cortical neurons respond vigorously to a limited range of stimulus orientations while their primary a erent inputs neurons in the lateral geniculate nucleus LGN respond well to all orientations Mechanisms based on intracortical inhibition and or converging thalamocortical a erents have previ ously been suggested to underlie the generation of cortical orientation selectivity however these models con ict with experimental data Here a scale model of a m by m region of layer IV of cat primary visual cortex area is presented in order to demonstrate that local intracortical excitation may provide the dominant source of orientation selective input In agreement with experiment model cortical cells exhibit sharp orientation selectivity despite receiving strong iso orientation inhibition weak cross orientation inhibition no shunting inhibition and weakly tuned thalamocortical excitation Sharp tuning is provided by recurrent cor tical excitation As this tuning signal arises from the same pool of neurons that it excites orientation selectivity in the model is shown to be an emergent property of the cortical feedback circuitry In the model as in experiment sharpness of orientation tuning is independent of stimulus contrast and persists with silencing of ON type sub elds The model also provides a uni ed account of intracellular and extracellular inhibitory blockade experiments which had previously appeared to con ict over the role of inhibition It is suggested that intracortical inhibition acts non speci cally and indirectly to maintain the selectivity of individual neurons by balancing strong intracortical excitation at the columnar level