For weeks after birth, a newborn mouse is blind, with eyes that have yet to open. But to prepare the animal to see when its eyes do open, neural circuits in the brain’s visual system must begin developing. This same situation, which is in place before birth in humans, is a scientific puzzle, because the proper development of many brain regions involved in vision generally requires sensory input through the eyes.New research shows that waves of spontaneous neural activity in the retinas of still-closed eyes in mice are necessary to properly wire up the brain: when their eyes finally open, the mice are able to see. “If you interfere with this activity, the wiring details are all wrong,” says Michael C. Crair, Ph.D., William Ziegler III Professor of Neurobiology and professor of ophthalmology and visual science.As reported in the October 11 issue of Nature, Crair’s team simultaneously recorded the activity of neurons in the eyes and brain of newborn mice. They found that waves of activity in the retina were relayed through the brain and produced corresponding activity in the visual cortex, where information from the retina is processed. This occurred for at least a week of a mouse’s life.The work sheds light on how similar neural activity in unborn fetuses shapes the human visual system.