Vision and the establishment of direction-selectivity: a tale of two circuits.

Direction-selective neurons, which respond selectively to motion in one direction, have been characterized in visual circuits across many species. Recently, the development of these directional neurons has been explored in both retina and primary visual cortex (V1). The development of direction-selective cells in V1 requires visual experience. In contrast, direction-selective ganglion cells in retina are present at the age of the earliest light responses. The vision-independent signals guiding the asymmetric wiring underlying retinal direction selectivity remain unknown. The details of how retinal and cortical circuits extract motion information could explain their differing requirements for visual experience in development.