For decades, neurobiologists have believed that so-called ocular dominance columns--neat columns of brain cells that respond to visual activity from one eye or the other--form as a result of visual activity. Now, in work described on page 1321, neuroscientists report that ocular dominance columns in ferrets appear long before the columns can be modified by visual experience. They propose instead that innate molecules that guide growing axons to their locations in the developing brain may be primarily responsible for building these columns. But others contest the conclusion that neural activity is not required for constructing the columns, arguing that there are other explanations for the researchers' findings.