Deep white matter is the name given to a part of the brain that is found between the cerebellum and the brain stem. It was erroneously considered to be passive tissue earlier, but research into this area of the brain has revealed that it is responsible for regulating a variety of unconscious body functions such as blood pressure, body temperature and heart rate. Thought to influence the expression of emotion, deep white matter is thought to play a major role in the onset of many puzzling conditions such as Alzheimer's disease, multiple sclerosis and vascular dementia. Also known as diencephalon, its major function is to relay signals between the nervous system and the gray matter that surrounds it.
Composed mostly of bundles of mylelinated axons, deep white matter functions as the brain's transmission infrastructure. Information is typically sent from neuron to neuron through projections of the nerve cells known as axons. White matter contains bundles of myelinated axons, or axons surrounded with white fatty tissue called myelin. They, in turn, act like an insulating sheath, helping nerve impulses to travel faster along the axons. Gray matter of the brain, in contrast, contains non-myleinated axons and capillaries.
Messages are transmitted to different parts of gray matter in the brain through deep white matter. This area of the brain is very resilient and can adapt to damage by finding different routes that bypass the damaged areas of white matter. Diseased white matter hampers the ability of the brain to function fully. White matter is responsible for the proper sharing of information and co-ordinating the operation of various regions of the brain, while the brain's gray matter performs functions like calculating and thinking. In diseases like Alzheimer's, deep white matter is significantly altered over time with the progression of the disease.
Comprising about 50% of the total brain tissue, white matter is white in color due to the presence of myelin, which consists mostly of lipid tissue with capillaries. Grey matter is more pinkish in color due to the presence of a large number of blood capillaries. Only partially present at the time of birth, the amount of myelin found in the brain increases through out adolescence and a person's 20s. The amount of myelin growth, timing, and the extent to which it is completed is thought to affect functions like self-control and learning, and may even be partially responsible for mental disorders like schizophrenia.