White Matter: Everything you need to know

Everyone has probably heard of “white matter” and “gray matter” before when people talk about our brain. This article focuses on the light-colored matter, what it is, why it’s called “white”, the difference between the two “colored” matters, what it’s made of, what its structure looks like, what its purpose is, and some weird facts about it!

White matter
White matter

What is white matter? What does it mean?

White matter is the subway of the brain. It connects the different parts of gray matter in the cerebrum to another. Like a subway/metro, this type of matter remains underneath it all (the surface in life, gray matter in the brain) and this underneath part is filled with different passages, links, and paths to take- each one with a different destination and purpose.

It’s known to be white because this type of matter is myelin rich. Myelin is a fatty-rich substance that causes the matter to appear white. In reality, the matter is a pinkish-white.

In adults, the matter is about 1.7-3.6% blood and takes up about 60% of the brain!

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What is the difference between gray matter and white matter?

Our nervous system is divided into two different parts: the central nervous system, and the peripheral nervous system. Within the central nervous system, there are two parts: the brain, and the spinal cord. Within the brain, there are another two parts: white matter and gray matter. Gray matter takes up only about 40% of the brain while white matter takes up a whopping 60%.  

More differences between the two matters:

  • White matter is made up of fibers (the nerves) while the gray matter is made up of nerve cell bodies (the little cells that transfer and bring information to neurons).
  • Gray matter has no myelin sheath while white matter is myelinated. Myelin is a lipid-rich (fat-rich) material that surrounds the nerve fibers (the axon) in some of the brain’s nerve cells. Myelin forms an electrically insulating coating.
  • White matter has myelin, which appears white. Gray matter lacks myelin and therefore has no white tint to it.
  • White matter allows for communication to pass to and from the gray matter areas while gray matter actually stops processing communication.
  • Gray matter peaks development in a person’s 20s while white matter develops longer and peaks during one’s middle-age years.
  • White matter is buried within the brain- deeply. Gray matter is only of the surface, known as the cortex. Within the spinal cord, it’s the opposite: white matter is on the outside insulating while the gray matter is at the core of the cord.

The composition of white matter- what’s it made of?

White matter is a substance that is made up of bundles. Bundles that connect to the gray areas of the brain (where the nerve cell bodies are located) to each other and the matter carries nerve impulses between neurons. The myelin that lines the matter is like an insulator (think of the myelin as fat and think about how fat insulates). This insulation allows electrical signals to jump which increases the transmission speed of all nerve signals.

Structure of white matter

White matter is located in the deep parts of the brain and the outside of the spinal cord. Its tissue passes messages between different areas of gray matter within the central nervous system. This type of matter takes up the deepest parts of the brain. Where the gray matter isn’t (everywhere besides the cortex and top part of the brain), is where the white matter is. The myelin-rich matter is also located on the surface of the spinal cord and works as a form of fatty insulation to help protect the spinal cord and keep it functioning properly. Our light-colored matter structure can change depending on our environment- if we’re stressed (especially chronically stressed), if we’re happy, etc. Take a look at how this matter affects martial arts or musicians!

What is the purpose of white matter?

The whole purpose of the fat, lipid-rich matter is to help our brains work properly by connecting the information we take in and diverting it to different brain areas.

People who have autism have been found to have white matter abnormalities- mostly that the tracts and pathways in this type of matter failed to reach distances far away from the cortex in the brain. Thinking of this in terms of a metro/subway, this train didn’t travel very far and had to stop.

What happens when you have too much? Having too much of this matter shows up on brain scans as white spots on the brain. This over-excessive matter is known as white matter hyperintensities, nonspecific white matter changes, unidentified bright objects (UBO), or high signal intensity areas (HSIA). These spots are often located by the ventricles. However, there is no conclusion among neurologists how much of this light-colored matter is too much. These spots show up with a stroke, depression, cognitive decline, high blood pressure, diminished physical function, and narrowed blood vessels.

What is white matter disease of the brain?

White matter disease is a condition that targets the small blood vessels that thrive deep within the brain. These teeny tiny vessels and arteries harden which make it difficult for nutrients and information to access the cells within the light-colored matter. This happens due to the process of aging. It can also be caused due to long-term hypertension, smoking, chronic blood vessel inflammation, blood vessel problems (heart trouble, strokes), Parkinson’s, high cholesterol, and diabetes.

Before, it was thought that this disease only harmed the speed of thinking. However, now it’s been found that there are eight cognitive deficits that are associated with the disease which have revealed a widespread effect on the brain. These deficits include visio-spatial construction, language ability (and disability), and delayed memory. It makes sense considering that healthy matter helps us think fast, walk straight, and not fall down. The disease causes true cognitive damage and actually contributes to Alzheimer’s and vascular dementia.

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Studies on white matter

Without the myelin in the white matter, our motor skills and our cognitive skills would be next to nothing. Myelin is critical for our day-to-day functioning. It’s thought that the difference in this matter shows a difference in intelligence. It’s also thought that it shows a difference in certain psychiatric conditions.

It’s been found that short-term meditation actually changes the matter content in the anterior cingulate part of the brain. The anterior cingulate cortex (ACC) forms part of the neural network that implicates the development of self-regulation. Using integrative body-mind training (IBMT), which is a form of Chinese medicine, actually increases the activity within the anterior cingulate and it improves the brains self-regulation. Perhaps IBMT could even help reduce or prevent various mental disorders such as Alzheimer’s.

Our language ability and whether or not we dominate with our left or right hand has to do with an asymmetry between the cerebral cortex (which contains gray matter) and connectivity (full of white matter).

There’s a strong connection between breastfeeding and white matter growth in infants. Breast milk increases a child’s myelination (the fatty substance that makes up the white-ish matter). This increase causes the overall matter content in a child’s brain to grow. It’s been shown that breastfed infants have an improved brain development by age two.

While white matter can heal from damage such as a concussion, cerebral palsy, or multiple sclerosis, scientists have recently discovered that there are roadblocks that prevent this light-colored matter from healing. According to the study, there is a molecule that triggers a route, a pathway if you will, that is used by the immune system to help prevent any extreme damage. However, that molecule could also be contributing to chronic white matter injury by blocking the repair operations completely.

In a study done on 613 adults with an average age of 45.4 years who were enrolled in the CARDIA (Coronary Artery Risk Development in Young Adults) program, it was found that short sleeping durations are associated with “worse markers for light-colored matter integrity in midlife”. What does that mean? Well, it means that adults who have mid-life differences in the light-colored matter might have poorer sleep than adults whose matter stays relatively unchanged.

Depression can alter the brain’s white matter structure. That means that the circuitry that helps the brain communicate and is responsible for the overall function is toyed with. The study that found this mapped the brain structures in over 3,000 people. The researchers found that there was a change in white matter integrity, a fancy way of saying “the measurement of the brain’s white matter quality”, for those of the 3,000+ participants that reported having symptoms of depression in comparison with participants who didn’t report the symptoms.

There is a connection between Obsessive Compulsive Disorder (OCD) and matter quality. This study found that myelination changes (changes in the fatty white substance that makes up the lighter-colored matter)in the occipital and temporal regions of the brain are associated with OCD. The study concluded by saying that the pathogenesis of OCD might include changes in myelin in the front-striato-thalamic circuit, and also in the temporal and posterior regions.

Overall, considering that this beautiful matter takes up about 60% of the brain, many researchers agree that there needs to be a lot more research done on it.

Weird facts about white matter

  • White matter isn’t actually white- it’s a pinkish-white color.
  • Although men have less gray matter than women, men actually have more cerebrospinal fluid and great white matter.  
  • The white in the matter comes from the myelin sheath that is really just a fatty protection for the brain and spinal cord.
  • If a part of the matter is damaged, the brain is sometimes able to find a different route to replace the severed connection in order to keep the information process going smoothly.
  • It’s possible that our white matter can vanish completely if we have the genetic disorder Vanishing White Matter Disease (VWM).

Let us know what you think in the comments below!

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