Change in the Brain's White Matter

R. D. Fields
2010 Science  
Gray matter" is only one of two types of brain tissue; the other "white matter" is rarely mentioned. Yet white matter makes up half the human brain and has not been thought to be important in cognition or learning outside the context of pathology. That view could change. Imaging and cellular and molecular studies are revealing white matter plasticity with possible implications for normal cognitive function and psychological disorders. White matter, which lies beneath the gray matter cortex, is
more » ... omposed of millions of bundles of axons (nerve fibers) that connect neurons in different brain regions into functional circuits. The white color derives from the electrical insulation (myelin) that coats axons (see the figure) . It is formed by nonneuronal cells, oligodendrocytes, which wrap up to 150 layers of tightly compressed cell membrane around axons. Myelin is essential for high-speed transmission of electrical impulses, and its damage can impair conduction and consequently, sensory, motor, and cognitive functions. The human brain continues to undergo myelination until at least the third decade of age, and the frontal regions of the cerebral cortex, which carry out higher-level executive functions, are the last to become myelinated.
doi:10.1126/science.1199139 pmid:21051624 pmcid:PMC3201847 fatcat:n7fdnznehzgrjk456f2cyfzagi