Knowing what's going on inside your head

Brain growth and development

Knowing what's going on inside your head

Brain growth and development


Did you know that brain development plays a major role in how you handle your emotions 😲 ?

Mood swings, irritability, impulsiveness… we make a lot of observations about teen behaviour without really understanding what’s going on inside their heads. Let’s zoom in on the teenage brain to help you understand it better and see how it influences your everyday life.

What are the main stages of development in adolescence?

Adolescence has different phases, and your priorities and state of mind change throughout. This is partly explained by the fact that teen brain development doesn’t stop until around the age of 25.

During high school, friends start to play a more important role in your life🤝.

It’s a time when teens start being concerned about their popularity, as well as about choosing friends who have shared experiences and common interests. It is often through our friends that we start to define our values and form a deeper understanding of who we are.

This is also the time when teens become more independent: we start going out on our own more and have more freedom to choose what we eat, what we do, and when we sleep. It’s also during Grades 9, 10 and 11 that we discover our sexuality, form deep friendships, commit to different causes and, for some, get our first job.

As the brain becomes more and more capable of short-, medium- and long-term planning, we become better equipped to make gradual decisions about the life we want, the education 👩‍🎓 that interests us, what we want to do when we grow up, etc. As teens develop, we become increasingly able to gauge the consequences of our actions and experiment with new things so that we can, one day, become an adult👨‍💼👩‍💼.

What’s the brain’s role in all these changes?

Contrary to what you might think, not all areas of the brain develop at the same time. Development starts at the back of the skull and moves forward. More specifically, the brain begins its development at birth, at the back of the skull, at the amygdala—the region responsible for emotions and physical coordination—and ends at the front, at the prefrontal cortex. This is the part of the brain that controls our impulses, reasoning, planning, deduction and judgment.

When we talk about development of the regions of the brain, we’re really talking about the connections between neurons in each region. This connection is made through the myelin sheath that envelops the neurons: the role of myelin is a bit like the role of Bluetooth between a cell phone and speakers. By the time you’re 25, all of the connections between neurons will have been made.

Studies on brain chemistry suggest that it’s these major changes in the brain that are responsible for the fact that you sometimes feel more intense emotions or are irritable.

The progressive development of the amygdala up to the prefrontal cortex also explains why you might find yourself making impulsive decisions without thinking about the consequences. It also explains why you’re able to put your whole heart into a cause, invest yourself deeply in friendships, and keep an open mind when discovering something new.

As you grow up, the connections between the neurons of the prefrontal cortex complement each other, allowing you to better gauge the consequences of your actions and therefore plan better and judge what is good or bad for you. As a result, you progressively gain autonomy and are increasingly able to make your own decisions.

The teenage brain explained: Why adolescence is a party for your brain

Adolescence is the stage when your brain has 100% of its potential, allowing you to learn very quickly—especially when the learning is pleasurable. This means it’s the time when you’re best equipped to push yourself and try new things. It’s also the ideal time to discover new ways of living, meet new people, test your limits, and develop your independence. Friendships, romantic relationships, and new encounters are likely to inspire you and help you form your perspective—perhaps prompting you to defend certain causes that you care about or to push for changes in society.

So what do you need to look out for?

Since your brain is capable of learning very quickly when it gets pleasure from the experience—for instance, with music or sports—it can also be more vulnerable to drugs during this stage than in adulthood.

Alcohol, cigarettes, cannabis, and synthetic drugs: the brain adapts to all of them very quickly as new learning. The brain can also have great difficulty letting go of them, even in adulthood. Remember that all drugs, even so-called “soft” drugs, have a lasting effect and may prevent the brain from developing fully. Regular drug consumption can have this effect.

Between the ages of 14 and 17, the development of your brain makes it difficult for you to manage stress and emotions like an adult. This makes you more vulnerable to mental health problems when faced with difficult situations, such as failing grades, breakups, bullying, etc. This vulnerability is heightened by fluctuating self-esteem and the tendency to only see the negative when faced with an obstacle. It should come as no surprise that adolescence is a period when mental illness, such as depression, is more common.

If you’re sometimes overwhelmed by your emotions and feel like you’re losing control, you can:


Follow simple everyday tips to maintain your mental health.

Learn more

Understand what's happening

Find out how to better understand what’s happening if the way you’re feeling doesn’t change.

Learn more

Talk 🔊 to the people around you

Talk to the people around you.

Learn more

Need to talk about how you feel?

Speak with a Tel-Jeunes worker: it’s anonymous, free and accessible 24/7


Le développement des enfants et des adolescents dans une perspective de promotion de la santé et de prévention en contexte scolaire par l’Institut National de santé publique de Québec, 2017

Co-written with Dr. Benoît, psychiatrist, Expertise NeuroSciences