Scientists have found more clues about the evolving brains of baby mammals as eyesight comes online. Using an imaging system to get neuron-level resolution, they showed how one specific brain circuit -- the 'ventral stream' -- in mice came online immediately after birth, but another circuit -- the 'dorsal stream' -- needed visual stimuli in order to mature. The experiments have helped to unveil how early-in-life visual experiences -- simply trying to see -- sculpt a particular subnetwork of brain circuitry we need in order to see properly.