Multiple sclerosis is a progressive, disabling illness in which the body’s immune system attacks myelin, an important tissue of the nervous system. Myelin acts like insulation around nerve cells, helping them to conduct the electrochemical signals they use to communicate. Researchers use images like this one, which reveals the web-like structure of myelin in the mouse brain, to study how environmental factors such as viral infection might contribute to the disease process of multiple sclerosis and suggest better treatments.