Glossary
White matter
What is white matter?
White matter contains axons, many wrapped in myelin, and supporting cells. It connects brain regions and helps coordinate signals between them. Its pale appearance comes largely from myelin.
How myelin supports communication
Myelin forms electrical insulation around axons and changes how nerve impulses travel along them. It helps increase conduction speed and affects when signals reach distant regions. Timing matters when several regions must exchange information during a task.
White matter and gray matter
Gray matter contains many cell bodies as well as other neural structures. White matter contains axons and supporting cells.
Major tracts
- The corpus callosum connects the cerebral hemispheres.
- The arcuate fasciculus participates in language-related connections.
- The cingulum is another major bundle connecting regions involved in several functions.
Imaging
Diffusion imaging, including diffusion tensor imaging (DTI), characterizes properties related to white-matter organization. A measure called “integrity” does not identify one cellular mechanism by itself.
Example: disrupted communication after injury
Damage affecting white-matter axons or their myelin can disrupt communication between regions. After a brain injury, difficulty coordinating a task that draws on several regions could therefore involve damaged connections. That is a possible contribution to investigate, not a diagnosis based on task difficulty alone. It does not establish that gray matter is unaffected or that a particular imaging measure has identified the cellular damage.
Why it matters
Communication between regions matters alongside activity within them. White-matter properties contribute to cognition without fully determining an individual's ability.