What is White matter?
White matter consists of myelinated axon bundles that connect different brain regions, forming the brain’s long-distance communication infrastructure. It contrasts with gray matter (cell bodies) and is named for the white color of the myelin sheaths.
How it works
White matter tracts carry signals between brain regions at high speed, enabling the coordinated activity of distributed neural networks. Major tracts include the corpus callosum (connecting the two hemispheres), the arcuate fasciculus (connecting language areas), and the cingulum bundle (connecting components of the default mode network). White matter integrity is measured using diffusion tensor imaging (DTI) and declines with aging, traumatic brain injury, and neurodegenerative diseases. Reduced white matter integrity is associated with slower processing speed and cognitive decline.
Applied example
A person with a traumatic brain injury who has difficulty with complex tasks despite normal intelligence may have white matter damage that slows communication between brain regions. The processing areas work fine individually, but the connections between them are impaired.
Why it matters
White matter is the brain’s wiring infrastructure, and its integrity determines how efficiently brain regions can communicate, explaining why connectivity is as important as regional function for cognition.
