White matter
Named for its pale appearance — the lipid-rich myelin sheaths reflect light differently from cell-body-dense grey matter.
The brain's wiring: bundles of myelinated axons that move information between regions at speed.
01Composition
White matter is composed of myelinated axons together with their oligodendrocyte support, plus astrocytes and microglia. Myelin — a lipid-protein membrane wrapped tightly around the axon — is what gives the tissue its characteristic pale colour and increases conduction velocity up to a hundred-fold.
02Function
It connects: cortex to cortex (association fibres), hemisphere to hemisphere (commissural), and cortex to subcortex (projection). The conduction speed and timing precision of these tracts shape cognition; even small changes in myelin thickness retune circuits.
03Clinical significance
White-matter disease is a vast clinical category, including multiple sclerosis (autoimmune demyelination), leukodystrophies (genetic), and small-vessel ischaemic disease in older adults. Diffusion MRI now allows non-invasive tractography of individual bundles in vivo.
Further reading
- [1]Fields, R. D. (2008). White matter in learning, cognition and psychiatric disorders Trends Neurosci. 31(7).
- [2]Filley, C. M. (2012). The Behavioral Neurology of White Matter (2nd ed.) Oxford UP.