The forest is a metaphor for the growing and changing teenage brain.

Brain Development During Teenage Years

As you likely observe every day, teenagers’ brains are ever-changing. From pre-adolescence to early adulthood, teen brains ‘remodel’ in ways that allow them to form meaningful friendships, develop a sense of self, personal values, and goals, and eventually to make plans, delay gratification, and make positive behavioral choices that will help them reach their goals. These are monumental tasks that take a lot of time, and trial and error for both teens and their brains to get right. This month, we are going to take a dive into the world of neuroscience to find out what allows teens to do these amazing things, and when these changes happen in development. As you read, keep in mind that just like early developmental milestones like walking and talking, every teen develops differently when it comes to these milestones too. If you have concerns or questions, you and your teen are in the right place, Joon's therapists are here to help! 

The Brain is a Forest

Throughout development our brains go through periods of creating connections and growing new cells and periods of ‘pruning’ away brain cells and connections–when maturing actually happens. This might seem odd that much of brain development happens through deconstruction, but it makes sense if we think about how many other natural wonders, like forests, develop. 

In infancy, our brains are kind of like a meadow with lots of room for growth. Throughout infancy and toddlerhood, we as parents scatter all sorts of seeds hoping that they will take root. Among thousands of other things, we teach our children how to communicate, what a friend is, and how to stay safe and healthy. Toddlers soak up these experiences, growing the beginnings or ‘saplings’ of important life skills. However, in addition to these life skills, kids also make a lot of connections that they won’t need (for example, what dirt tastes like or which color marker shows up best on the living room wall). These connections are like the weeds and even the wildflowers that fill a field before taller trees take over.  

As children leave toddlerhood and enter childhood, the brain shifts from sprouting new connections to pruning away relatively unused connections and strengthening important connections by wrapping them in a protective coating called myelin. In this way, important connections literally grow like expanding tree trunks getting stronger as they are used. Unused connections, like smaller trees on a forest floor, die off or are pruned away so they don’t use precious resources. 

By adolescence, our teens are actually losing about 1% of their gray matter every year. In the forest metaphor, the adolescent brain becomes more and more like a mature forest every day, strengthening and growing connections that are important to that teen’s daily life, and pruning out those that aren’t. Building strong brain connections related to important life skills is a monumental effort that takes many repetitions to get right. Just like a tree adds growth one tiny ring at a time, building the complex brain-based skills that develop in adolescence happens gradually, requiring lots of patience from us as parents and from teens themselves as development happens! 

Brain scans from age 5 through 20 show the hard work that adolescent and young adults are doing creating and strengthening connections (shown in blue) in their brains. Source:

Still Under Construction 

In addition to being characterized by periods of growth and pruning, brain development also happens in a general order from back to front or bottom to top, depending on how you are looking at the brain. Broadly, development starts with more ‘basic’ brain functions such as sleep and motor control where basic skills are developed in infancy, to complex brain functions such as regulating emotions, stopping impulses, and planning ahead, which develop well into early adulthood. This means that while adolescents have developed many skills, they are still very much hard at work developing others. Some of the most important skills still ‘under construction’ include executive functions and emotion regulation.

Executive Functioning 

The last part of the brain to develop fully strengthened and protected (myelinated) connections is the prefrontal cortex. The prefrontal cortex is responsible for ‘CEO tasks’ like planning, goal setting, breaking down large projects into manageable steps, self-monitoring work for errors, getting started on complex tasks, and organization. It is also responsible for emotional and behavior regulation, including inhibiting or stopping impulsive behavior. Taken together, these organizational and self-control skills are referred to as executive functions, and they are very much still under development in adolescence. In fact, the prefrontal cortex and executive functions don’t fully develop until around age 25! 

As with anything that we haven’t mastered yet, practicing these new skills is exhausting and can be frustrating. For example, if your teen is assigned a big book report at the beginning of the semester, they might have difficulty knowing where to start and might feel completely overwhelmed by the idea of tackling such a huge endeavor. They might even give up before starting. As a parent, you can serve as your teen’s ‘administrative assistant’ to their brains CEO by helping them break down tasks, plan ahead, and process frustration. Just as you helped your child build physical strength when they were learning to walk, now you can help them build strong executive functions by providing practical support and encouragement. 

As mentioned above, the prefrontal cortex is also responsible for impulse control self-regulation. Consequently, continued development of executive functions (along with developmentally normative limit testing) plays a big role in the risky behaviors that are so common in adolescence. While a wide range of risk behaviors are typical in adolescence, it is still important to set clear limits, discuss consequences and family values, and provide appropriate monitoring to keep teens safe.

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Emotion Regulation

In adults, the brain regions responsible for emotions (the amygdala) and for self-regulation and complex reasoning (the prefrontal cortex) interact to help us use emotions to experience and navigate the world. Our amygdala lets us experience emotions, while our prefrontal cortex makes sure no emotion gets too intense to handle, helps us choose how to express that emotion, and helps us understand others’ emotions. 

Since teens’ prefrontal cortices are still under construction, teens tend to ‘think with their feelings’ instead of using their prefrontal cortex to regulate emotions. You might already have several examples coming to mind of recent times when your teen has interpreted a situation based on their feelings and not ‘the facts.’ Because of the relative dependence on the amygdala over the prefrontal cortex, teens are more likely to misinterpret emotions in others, have large emotional reactions, and quickly act on emotions. This can lead to interpersonal conflict, personal distress associated with intense emotions, and impulsive emotional behavior that a teen wishes they could take back. 

As parents, it’s important for us to acknowledge that while teens emotional reactions may seem ‘over the top’ to us, the intensity of emotion that our teens are expressing is exactly what their brains are wired for them to feel at this point in their development. We can help by validating their emotions and giving teens extra time (which their developing CEOs need!) to regulate these intense emotions before trying to help them ‘solve’ the situation or providing correction. For additional details on how to do this, see last month’s article that includes tips on emotion coaching. 

Teen Brain Superpowers 

We’ve talked a lot about areas of brain development that are still developing in adolescence; however, teens also have characteristics that are unique to adolescence and that decrease into adulthood. These include intense social motivation, fewer barriers to creative problem solving, the ability to rapidly learn and adjust to new social contexts. Among other things these abilities help teens come up with inventive ideas that adults might not consider, advocate for social change, and teach us all how to use new technology! 

Teen Brains and Therapy

All of these factors mean that teens need different support than children or adults do when it comes to their mental healthcare. Teens can and should be given a level of autonomy in working towards their mental health goals, which we wouldn’t expect for younger children. At the same time, most teens need therapy to be structured to support their developing executive functions (i.e., reminders about appointments, a structured approach, skills that are easily accessible on their phones, etc) and to address the unique challenges of adolescence such as intense emotions and stress associated with all of the developmental tasks that adolescence entails. The good news is that Joon was built with this in mind!


April 27, 2021
Michelle Kuhn, PhD | Clinical Advisor

Michelle Kuhn, PhD | Clinical Advisor

Michelle Kuhn, PhD, is a licensed clinical psychologist who received her BA from The George Washington University and her PhD in Clinical Psychology from Seattle Pacific University. Dr. Kuhn provides services to children, adolescents, and their families, utilizing evidence-based behavioral and cognitive-behavioral approaches. She has specialized training in mood and anxiety disorders, suicidality and self-injury, attention and behavior problems, and trauma. Dr. Kuhn also researches new treatments for children and their families in the field of neurodevelopment disorders.

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