White matter connects the various gray matter centers of the brain together to form communication networks, according to the DANA Foundation. White matter is primarily made up of myelinated nerve cell projections called axons, which facilitate these networks and make up the bulk of the brain and spinal cord.
White matter is able to quickly relay messages from one section of the brain to another because its axons are heavily myelinated, according to VU University Medical Center. Myelin forms fatty sheathes around the axons, insulating the nerve cells; this insulation keeps the axons from short circuiting and increases the speed of nerve impulses.
White matter connects the various parts of the brain and spinal cord in three ways, according to Wikipedia. First, it can extend vertically from the cerebrum to the rest of the body via projection tracts. Second, it can cross the brain from one hemisphere to the other via commissural tracts. Third, it can connect different regions of the same hemisphere via association tracts.
Actual cognition occurs in the brain's gray matter, according to News Medical. Gray matter, in contrast to white matter, is made up of the cell bodies of neurons and unmyelinated axons. The synapses between neurons are also found in the gray matter, which is located on the surface of the brain.