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Counselling Corner


The Teen Brain

Lily Bowles
RECC Team Psychology Writer


Adolescence, the teenage years, and the transformation from child to adult is a tumultuous time full of physiological, psychological, social, and emotional changes. During these years, changes in growth and sex hormones elicit pronounced effects in the brain and body. The brain matures and shifts, reframing its ability to reason and plan as well as other essential functions. The massive flood of fluctuating hormones can also make for intense emotional cascades and volatility. Additionally, many mental illnesses first present themselves during this already difficult time. Here, we’ll examine some of the most significant and fascinating changes that go on inside the brain of a teenager.

The teenage years are, first and foremost, a time of growth in the brain. While the brain does not change much in overall size during these years, it undergoes significant shifts in terms of neurogenesis (the birth of new neurons) and synaptogenesis (the creation of new connections between neurons). The teenage brain can be described as highly “plastic.” Plasticity refers to the ability of the brain to mutate and change, often based on the environment or patterns of behavioural use. Because of this, the teen brain is particularly malleable, something that decreases with age. An old neuroscience adage is that neurons that “fire together wire together” and at no time is this more true than during the burst of growth and new paths forged during the teen years. This means that the teen years are a time where habits or behaviours (both good and bad) can become ingrained and hard to change later. This plasticity is part of why it is easier for young people to learn new things so such as a new instrument or language. Unfortunately, it also means their young spongey brains are more easily able to learn bad habits or addictions. Yet another reason that drug and alcohol use during this time is particularly harmful. However, this remarkable stage of plasticity also imparts an incredible capacity for resilience that we don’t always see in adult brains.

In addition to the growth and changes in the brain, hormones are flooding the bloodstream. A certain amount of emotional volatility during this time is normal, even expected, as the body learns to calibrate itself in the rush of a cocktail of new hormones that are constantly in flux. It can be hard to tell sometimes if certain behaviours or feelings are just the usual teenage angst or signs of something more serious. Interestingly, the vast majority of mental illnesses first present during the adolescent years. It is not known precisely why, but most psychiatric illness, including anxiety and mood disorders, psychosis, eating disorders, personality disorders, and substance abuse, seem to emerge between the ages of 11-18. In fact, 50% of mental illness begins by age 14, and three-quarters begin by age 24 (APA). If left untreated, these illnesses can have catastrophic effects on the quality of life for a teenager and beyond. Luckily, with early detection and intervention, most of these illnesses have excellent prognoses, and teens suffering from mental health problems can go on to lead happy and productive lives. Getting in the habit of seeing a mental health professional can have numerous benefits for teens. In addition to treating mental illness, many young people enjoy having an adult that is not their parent with whom they can be open and honest. A therapist is also a great resource to help teens to navigate some of the tough choices in their lives.

Speaking of choices, teenagers are notoriously bad at making them. That isn’t to say all teenagers make bad decisions, but when they do, it is often a result of the developing physiology of their brains. Adolescent brains are somewhere around 80% developed, and the remaining areas of the cortex develop over time from back to front. The very last section to finally develop is the frontal lobe, responsible for reasoning, planning, and judgment. Because of this delay, a teenager’s prefrontal cortexes, the areas of the brain responsible for what is called executive functions, self-control, and for thinking about the future, are not fully formed. These areas won’t be complete until much later in life, some researchers estimate as late as 25 or 30 years old! That means that while the rest of their brains, particularly areas associated with risk and reward, are hyped up on hormones, the part that tells the teen to slow down and consider the consequences of those actions is lagging. This is a recipe for risky decision making and poor foresight that, unfortunately, sometimes characterizes teen behaviours. This delay in the finalization of physiology is not an excuse for poor behaviour, but rather an explanation as to why sometimes even the best-meaning and formerly perfectly behaved teenagers can do reckless or impulsive things, especially when pressured by their peers.

The teenage years are a time of metamorphosis. The body and brain undergo massive restructuring and recalibration in order to mature and develop into an adult. At times these changes can be stressful and uneven. The transition from child to adult is not a smooth or seamless one, and nowhere is that reflected more acutely than in the body and brain. Learning about the physiological changes that happen during this time and having a loving support system can go a long way to helping take some of the burdens off of teens during this challenging but also unique and exciting time. Helping to establish a healthy lifestyle and encourage smart behaviours and decisions, as well as solid
communication skills, are gifts that will serve teens well throughout their lifetimes.


Harvard Magazine. (n.d.). from

Stanford Children’s Health. (n.d.). from

Giedd, J. N., Keshavan, M., & Paus, T. (2008).
Why do many psychiatric disorders emerge during adolescence? Nature Reviews. Neuroscience, 9(12), 947–957.

The Teen Brain: 6 Things to Know. (n.d.).

The Teen Brain in a Grown-up World. (n.d.).

Why Teenage Brains Are So Hard to Understand | Time. (n.d.).


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