Retinal input instructs alignment of visual topographic maps

Sensory information is represented in the brain in the form of topographic maps, in which neighboring neurons respond to adjacent external stimuli. In the visual system, the superior colliculus receives topographic projections from the retina and primary visual cortex (V1) that are aligned. Alignment may be achieved through the use of a gradient of shared axon guidance molecules, or through a retinal-matching mechanism in which axons that monitor identical regions of visual space align. To distinguish between these possibilities, we take advantage of genetically engineered mice that we show have a duplicated functional retinocollicular map but only a single map in V1. Anatomical tracing revealed that the corticocollicular projection bifurcates to align with the duplicated retinocollicular map in a manner dependent on the normal pattern of spontaneous activity during development. These data suggest a general model in which convergent maps use coincident activity patterns to achieve alignment.