Neuronal connections underlying orientation selectivity in cat visual cortex

How do neurons of the visual cortex acquire their acute sensitivity to the orientation of a visual stimulus? The question has preoccupied those who study the cortex since Hubel and Wiesel1 first described orientation selectivity over twenty-five years ago. At the time, they proposed an elegant and enduring model for the origin of orientation selectivity. Fig. 1A, which is adapted from their original paper and which contains the essence of their model, is by now familiar to most students of the visual system and to many others besides. Yet the model, and the central question that it addresses, is still the subject of intense debate. Competing models have arisen in the intervening years, along with diverse experiments that bear on them