Lifespan: The Revolutionary Science of Why We Age—and Why We Don't Have To

by David A. Sinclair

Instead of waiting for another year to see if the mice lived longer, Yuancheng suggested he use a mouse’s optic nerve as a way to test age reversal and rejuvenation. I was skeptical. “I’m not superoptimistic this will work,” I told him. “Optic nerves just don’t regenerate, unless you are a newborn.” The intricate network of cells and fibers that transmit nervous signals across our bodies is divided into two parts: the peripheral system and the central system. We’ve known for a long time that peripheral nerves, like those in our arms and legs, can grow back, albeit very, very slowly. The nerves of the central system, though—optic nerves and the nerves of the spinal cord—never grow back. Even those scientists who bucked convention, proposing novel therapies that could regenerate some aspect of the central system, have generally been circumspect about the potential for significant regrowth. Decades of work aimed at reversing glaucoma in the eye and spinal cord injury has had almost no positive momentum.