The human brain consists of gray matter and white matter. Both of these types of brain tissue are present from birth, but during the teen years, they go through major changes.
To help you understand the roles of gray matter vs. white matter in teenage development, this page explores:
The brain is made up of two main types of tissue: gray and white matter. We discuss these two types of tissue and their main functions in the sections below.
Gray matter is made up mostly of neuron cell bodies, in which any information that goes into the brain gets processed. You need it to interpret sensory information, emotions, and feelings, and to make decisions.
Along with cell bodies, gray matter also contains dendrites, which are branch-like structures that receive signals from other brain cells. These brain cells can be other neurons or supporting cells.
Because of a large concentration of neurons, the gray matter actually looks gray – hence where it gets its name. It is found in the outer parts of the brain. The external layer of the gray matter is also folded into ridges and grooves, which increases its surface area so more neurons can fit into the same amount of space.
White matter is made up mostly of axons. These are long, cable-like extensions that carry signals away from a neuron’s cell body to other neurons.
The axons in white matter are coated in myelin, a fatty substance that gives this tissue its whitish appearance. This fatty insulation allows electrical signals to travel between brain regions much faster and more efficiently than they otherwise would.
The job of white matter is to transmit information. It tends to sit closer to the center, beneath the outer layer of gray matter, forming the connective tissue that links different regions together.
The teen years bring the most significant structural changes the brain undergoes at any point in life. While the teen brain reaches close to its full adult size in early adolescence, the gray matter and white matter continue to change until well into the twenties. Below, we take a detailed look at the changes in brain anatomy during adolescence.
The gray matter follows an inverted U-shaped pattern of growth during which its volume increases until it reaches a peak around the onset of puberty. Then, it gradually decreases throughout adolescence and into early adulthood.[1]
The gray matter in different brain regions peaks and declines on its own separate timelines. The areas of the brain responsible for basic sensory and motor functions mature earlier than the prefrontal cortex, for example, which helps with complex reasoning.
The decline in gray matter volume happens because there is ongoing white matter growth. So, you’re not essentially losing brain content; it just shifts from predominantly gray matter to white matter.
The process by which gray matter declines is known as “synaptic pruning.”
During early childhood, the brain produces a huge number of connection points where brain cells communicate with one another – far more connection points than it will ultimately need. As we grow older, the brain eliminates the connections that are used less frequently and strengthens the ones being used more often.[2]
Any connections that you use heavily in teenage years, for example, the ones used for a particular skill or a way of thinking, tend to be reinforced. Therefore, synaptic pruning allows the brain to become more efficient as it gets rid of redundant connections.
The total white matter volume increases during teenage years in both males and females. Unlike gray matter, white matter growth does not peak and reverse in the same way; rather, it continues rising until early adulthood.
The white matter volume tends to peak later in males, around age 14.5 on average, compared to females (10.5 years on average).[3]
Myelination is the process behind continuous white matter growth. It causes the axons, the long fibers that carry signals between neurons, to become coated in the fatty substance we mentioned earlier – myelin. This insulation speeds up how quickly electrical signals travel between brain regions.
The process of myelination happens region by region at different times. The connections between the pathways linking the prefrontal cortex to other regions involved in emotion and decision-making continue improving in speed throughout the teen years.
All teens have the pattern of an overall decline in gray matter and an increase in white matter, but the rate at which this change occurs varies from person to person.
Girls generally reach puberty one to two years earlier than boys; therefore, the changes in brain development in girls also tend to happen earlier than in boys.
Those in the middle stages of puberty tend to show greater variability in brain development compared to those who are prepubertal.[4] Further, every teen’s individual biology also has an effect on the rate of transition from gray matter to white matter predominance.
So, there is no single fixed timeline that applies to all teens equally.
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The structural changes happening in the teen brain link up to shifts in their patterns of thinking and behaving.
As white matter increases, connectivity between different brain regions increases to support faster information processing. So, you may see improvements in reaction time and cognitive control as teens grow. Better insulation of brain wiring has a direct benefit for mental tasks that require quick, coordinated thinking, for example, holding several pieces of information in mind at once.
Gray matter volume changes also refine a teen’s ability to process information. Synaptic pruning makes more specialized thinking possible, which is reflected in a teen’s language skills, executive functions, and social skills.
Additionally, both gray matter and white matter work in coordination. As connections between brain regions strengthen through myelination, the gray matter areas those connections link together also reorganize at the same time.
It is due to these structural changes that teens gradually become better at planning ahead, managing emotions, adjusting to new situations, thinking through consequences, and so on.
Adolescent brain development is a popular topic online, but much of what circulates on social media is far from actual science.
Here are some misconceptions about gray and white matter in the teenage brain and what science says about them.
Early brain imaging studies from the late 1990s that tracked gray matter changes in children and teens only studied participants until around age 20. Researchers at the time estimated that brain development likely wrapped up in the mid-20s.
Newer data, however, suggests that network efficiency in the brain continues evolving into a person’s early 30s. So there’s no set birthday at which you can say that your brain has reached its full development.[5]
The gray matter decrease seen during adolescence primarily happens through synaptic pruning, which is the elimination of underused neural connections.
This is not a genuine loss of brain material or any of your abilities. Rather, it makes the rest of your brain connections more efficient.
Since gray and white matter research is often applied to different circumstances so casually online, many people assume a scan could tell you why a specific teen acted a certain way, or what they’ll do next. However, this is not how research works.
Research findings describe population-level patterns observed through many brain scans over time. They are not diagnostic tools for predicting one individual’s specific choices.
Different teens can have different brain development timelines, and besides their brain anatomy, their behaviors are also affected by environment, relationships, and personal circumstances.
The structural brain changes in teenage brains are partly why teens might exhibit higher degrees of certain behaviors. These behaviors typically include:
However, some of these behaviors may require professional mental health monitoring if they become exaggerated. Therefore, you might need to monitor your teen for the following signs while their brain is still developing:
Even though white matter and gray matter changes are a built-in part of adolescent brain development, the following factors support a healthy transition:
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The teenage years are the time when the brain undergoes extensive gray matter pruning and white matter growth. But, surprisingly, it is also when mental health conditions are most likely to first emerge.
A worldwide study of over 700,000 people found that 34.6% of individuals had a mental health disorder first diagnosed before age 14, 48.4% before age 18, and 62.5% before age 25.[8] This is the same stretch of years during which the brain goes through its most significant gray and white matter reorganization. Therefore, teen behavior during these years needs to be very keenly observed.
At Mission Prep Teen Treatment, we offer a variety of treatment programs delivered by licensed clinicians who understand adolescent brain development. Treatment is built on evidence-based therapeutic approaches, and we create individualized treatment plans for everyone.
Whether your teen could benefit from residential treatment at one of our locations in California or Virginia, or something more flexible like an outpatient mental health program or virtual telehealth to treat their mental health concerns, our team can help.
Mission Prep Teen Treatment accepts insurance and is in-network with most major providers. We are happy to help you check your insurance coverage for mental health care.
Contact us online or call 866-901-4047 to speak with a caring member of our team who can answer any questions you might have. Reach out for a free, no-obligation conversation.
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