nerve firings grow myelin, myelin controls impulse speed, and impulse speed is skill. Myelin doesn't make synapses unimportant—to the contrary, Fields and other neurologists emphasize that synaptical changes remain key to learning. But myelin plays a massive role in how that learning manifests itself. As Fields put it, “Signals have to travel at the right speed, arrive at the right time, and myelination is the brain's way of controlling that speed.”
