白質
Gray matter is responsible for generating nerve impulses that process brain information, and white matter is responsible for transmitting that brain information between lobes and out through the spinal cord. Nerve impulses are transmitted by myelin, a fatty material that grows around a cell. White matter has a myelin sheath (a collection of myelin) while gray matter doesn't, which efficiently allows neural impulses to move swiftly along the fiber. The myelin sheath isn't fully formed until around ages 24–26. This means that adolescents and young adults typically learn differently, and subsequently often utilize visual aids in order to help them better comprehend difficult subjects.