The Song of the Cell: An Exploration of Medicine and the New Human

by Siddhartha Mukherjee

Neural connections between the eyes and the brain are formed long before birth, establishing the wiring and the circuitry that allow a child to begin visualizing the world the minute she emerges from the womb. Long before the eyelids open, during the early development of the visual system, waves of spontaneous activity ripple from the retina to the brain, like dancers practicing their moves before a performance. These waves configure the wiring of the brain—rehearsing its future circuits, strengthening and loosening the connections between neurons. (The neurobiologist Carla Shatz, who discovered these waves of spontaneous activity, wrote, “Cells that fire together, wire together.”) This fetal warm-up act—the soldering of neural connections before the eyes actually function—is crucial to the performance of the visual system. The world has to be dreamed before it is seen.