What Are Gray Matter and White Matter?

White matter and gray matter are distinct types of areas of the brain. Both are essential for thinking skills, emotions, and muscle movement.

You may have heard the terms “gray matter” and “white matter” during discussions about the brain. But what’s the difference, and are they actually gray and white? Do they differ in other ways?

Gray matter and white matter do have different responsibilities, but both are essential for healthy cognition (thinking), movement, emotional regulation, and more.

Knowing the differences between gray and white matter may be especially helpful if you or someone you know develops a condition that directly affects one or both of these critical features of your or their brain.

Read on to learn more about gray and white matter and what you can do to preserve or improve their health and function in the years ahead.

What is gray matter?

Gray matter consists of densely packed neurons (nerve cells). It’s called “gray” because the concentrations of neurons give it a grayish, pinkish color when stained with certain materials. These cells are directly involved in many thinking skills, emotions, and muscle movement.

Where is gray matter located?

Gray matter tissue is found in your spinal cord and brain . It makes up most of your brain’s outer layer, especially in your cerebral cortex and cerebellum . You can also find some gray matter deep in your cerebrum and in the inner section of your spinal cord.

What does gray matter do?

Gray matter processes information and allows you to control thoughts and memories, feelings and emotions, sensory input, and muscle movement.

What is white matter?

White matter primarily consists of axons (nerve fibers) that connect neurons. The axons are wrapped in a myelin sheath , which gives them their white color. The myelin sheath also boosts the transmission and speed of signals traveling between neurons.

Where is white matter located?

White matter, which is made up of countless thin strands that act like communication cables, is mostly found deep within your brain. The outer portion of your spinal cord is also made up of white matter.

What does white matter do?

White matter carries signals between areas of gray matter. It allows you to learn and recall information, stay balanced when walking, and respond with appropriate feelings and behaviors to various emotional circumstances in your life, among other functions.

What diseases affect gray and white matter?

Gray matter and white matter rely on steady, robust circulation to nourish them with oxygen-rich blood. Lack of blood flow, even for a short time, can damage or destroy neurons and axons. This can occur during a stroke or if you experience cardiac arrest and your heart stops beating temporarily.

Gray matter diseases

One of the main health problems affecting gray matter is the buildup of tau and amyloid beta, two toxic proteins that are hallmarks of Alzheimer’s disease .

Another gray matter disease is Parkinson’s disease , which results from nerve damage that causes levels of dopamine (a brain chemical responsible for muscle control) to drop significantly.

Severe head trauma may also damage or destroy gray matter.

White matter diseases

Chronic disease of the small blood vessels in your brain, called microvascular ischemic disease , can cause interrupted blood flow, causing many silent strokes over several years. This can lead to shrinkage of your white matter, which is a type of white matter disease .

Causes include high blood pressure and atherosclerosis , the buildup of plaque in your arteries , causing a restriction of blood flow.

Another disease that can affect white matter is multiple sclerosis (MS) , which destroys the myelin sheath around nerve fibers.

Other white matter diseases include:

• Lyme disease
• Baló concentric sclerosis
• tumefactive demyelinating lesions
• Marburg MS and Schilder MS
• neuromyelitis optica (Devic disease)
• acute disseminated encephalomyelitis
• acute hemorrhagic leukoencephalopathy (Hurst disease)
• progressive multifocal leukoencephalopathy
• cerebral adrenoleukodystrophy

Severe head trauma can also damage white matter.

Frequently asked questions

What is the main difference between gray matter and white matter?

White matter and gray matter are both made up of neurons, which contain a cell nucleus, myelinated axons, and dendrites. White matter is more heavily myelinated than gray matter, which gives the types of regions different appearances when viewed with a microscope or on certain imaging tests.

Is it better to have more gray matter?

Having more gray matter is associated with greater thinking skills and memory. Age-related brain volume shrinkage often affects gray matter, which in turn affects functions such as memory and attention.

Can you rebuild gray matter?

For many years, scientists assumed that new brain cells stopped developing in childhood, but studies have suggested that this theory is incorrect.

A 2018 study suggests that regular physical activity may play a key role in new brain cell development and that nearly 80% of gray matter may be able to be changed by exercise. A 2020 study suggests that brief sessions of mindfulness meditation may also boost the production of new brain cells, which can increase gray matter volume.

How can I increase white matter in my brain?

A healthy lifestyle supports the best gray matter and white matter function and volume. A 2021 study , for example, suggests that an hour of exercise a day can significantly improve white matter function and strength within 6 months.

At what age does white matter start to decline?

Like gray matter, white matter tends to shrink as you get older. According to a 2017 review , white matter begins to decline more rapidly after 60 years of age.

Takeaway

Gray matter and white matter work together to keep your brain functioning and keep you able to perform everyday activities.

The following table summarizes some of the key differences between gray and white matter:

Characteristic	Gray matter	White matter
Location in your brain	mostly on the surface	mostly deeper below the cortex
Components	neurons	heavily myelinated neurons
Age of peak development	fully develops during your 20s	peaks in middle age

Though we think of them as distinct areas, damage to one area can affect the other. Regular exercise, a healthy diet, and sufficient sleep are three important steps you can take to preserve white and gray matter, or at least slow age-related loss in these areas.