When we think of the brain, most of us think of the grey matter that makes up the blanket-like outside layer of the brain – called cortex. Grey matter has long been attributed to the higher functions of the brain, including learning and perception. Another critical part of the brain is the White Matter, which is just as important of the grey matter.
What is White Matter?
White matter has essentially been in the back seat for much time. It was mostly ignored while grey matter was studied and touted for its role in learning. But today white matter has made its way to the forefront, receiving recognition for its vital roles in the brain.
Under the surface of the grey area, billions of bundles of nerve fibers (or axons) are tightly wound, connecting neurons found in the gray matter into circuits. These fiber bundles are white because they are coated with myelin, a fatty substance which appeared lighter than the grey matter to the old anatomist who named this part of the brain. White matter is make up of nerve bundles which carry information – in the form of electrical impulses – from neurons from part of the brain to the other parts of the brain. The myelin sheath around these nerve bundle is somewhat similar to the insulating coverings of the electrical wires.
When nerves are myelinated, their electrical impulses can travel much faster than nerves that are naked. Myelination enables the electrical signals to travel down the nerve bundles at a speed of 200-300 miles per hour, much faster than the speed in the non-myelinated nerve bundles of 1-2 miles per hour. Fast and efficient transmission of signals from one part to another part of our brain is essential to all of our cognitive function, especially for learning and memory.
Millions of neurons within the brain must be linked with activity in order for a coherent memory to be produced – a memory that interweaves many different senses and stored experiences. Since learning requires many different aspects of experiences, signals from different parts of the brain need to be combined and analyzed. In recent years, scientists have come to appreciate that injury to the “white matter” system in the brain – which can happen due to lack of sufficient blood flow in the brain – can seriously harm our ability to learn and remember; such white matter deterioration can also increase our risk of developing Alzheimer’s disease.
Another fascinating new discovery is that the white matter portion of our brain can actually change with our daily habits (such as smoking or exercising). People who are obese, have high blood pressure, smoke, and have a stressful life style have more white matter injury with aging than those who are fit and healthy. Evidence has shown that changes in white matter structure also takes place during learning. When we use our brains to learn new things (such as learning a new language or practicing a new musical instrument) we increase the amount of white matter in our brain. The amount of change was proportional in one experiment to the number of ours practiced.
One study found a relationship between the structure of white mater and IQ, suggesting that “cognitive function correlates with greater fiber organization,” according to study authors.
White matter continues to be studied and further understood. It is now known that it is an integral to brain function just as its grey matter counterpart. It is involved in learning and helps us with learning new skills and forming memories. And the more we learn, the more white matter we build in our brain. As research continues, the picture will undoubtedly become clearer.
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This blog was written by Mrs. Courtney Cosby and edited by Dr. Majid Fotuhi.