A detail for neuroscience fans: Axons are “myelinated,” wrapped in an insulating sheath made of cells called glia. It speeds up neuronal communication for reasons that I manage to teach confusingly in a class of mine year after year. The wrapping is fatty and whitish in color, and as a result, parts of the brain mostly made up of myelinated cables are termed “white matter,” while areas packed with the unmyelinated cell bodies of neurons are termed “gray matter.” White-matter freeways connecting gray-matter city centers,
