The goal of this talk is to present the basis of the visual system in mammals and more precisely how long-range connections in the primary visual cortex can influence local cortical activity as seen in optical imaging experiments for example. It is known that the representation of contours in the primary visual cortex is locally organised around “pinwheels” and possesses an approximate Euclidean invariance when only local connections are considered. We will then briefly show how to use these ‘ingredients' to reproduce visual hallucinatory patterns.