White Matter Matters a Lot

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White Matter Matters A Lot

When it comes to your brain, you probably have read all about the brain's "gray matter." Gray matter, so called because of its distinctive color, is composed of cell bodies of nerve cells and is responsible for memory storage. "White matter" also is in the brain and consists of millions of long filaments (axons) coated with a fatty white substance called myelin that extend from the cell bodies. This white matter fills half of the brain and helps transmit electrical signals that carry the important messages between neurons from one brain region to the other.

White matter has long been a mystery to neuroscientists as well as to the surgeons who operated on the brain. The main thought was that myelin -- which looks like an outstretched, elongated finger when viewed under a microscope -- was simply insulation and that the filaments inside were passive passageways. Only in the past decade have researchers begun to better understand the critical role of white matter in helping a person master a variety of mental skills.

Johns Hopkins scientists have discovered to their surprise that nerves in the mammalian brain's white matter do more than just ferry information between different brain regions. In fact, they process information the way gray matter cells do, and assist brain regions to work well together. The discovery in mouse cells, reported in a cover story in the journal Nature Neuroscience, shows that brain cells "talk" with each other in more ways than previously thought.

Researchers in Europe have also noted that the maturing of the brain from childhood to adulthood, and experience at an early age (learning a foreign language, how to play a sport, ride a bike, play an instrument) influences the formation of myelin, strengthens neuronal connections, speeds the learning process, and improves cognition. Damage to the myelin, on the other hand, can impair mental abilities.

Damage to the brain's white matter has also been found to be an indicator of potential memory problems and dementia. Dutch researcher Niels Prins, M.D., has discovered that elderly people with damage to the small blood vessels in the brain have a greater chance of developing dementia or depression.

Elderly people with serious white matter abnormalities and infarcts taking part in Dr. Prins's study were found to deteriorate more quickly in their cognitive functioning than peers with fewer abnormalities. In particular, the processing of information was worse in the group with more white matter lesions and infarcts. This group also had an increased risk of developing dementia and depression.

Over a period of three years, one-third of the elderly people he investigated exhibited an increase in white matter lesions. These individuals had an increased likelihood of experiencing a stroke and a faster decline in their cognitive functioning. Furthermore, a significant increase in the number of abnormalities in the white matter increased the risk of dementia and depression.



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