The teenage years. They can be some of the most dramatic and irrational times of our lives. We get to high school and before we know it, there is a dramatic change in our attitudes. Our responses are more emotional. And of course, we try to navigate the complexities of sexual development.

The teenage years are one of the most pivotal times in our lives. Why teens act the way that they do have been a topic of significant amounts of research.

As you might expect, hormones play an important role in the teenager’s brain, but what else is going on in there? Are there other factors at work? Is a teenager’s brain more influenced by outside factors? Here’s what the science tells us.

Still Developing Brain

Contrary to popular belief, the brain does not stop developing in infancy. The growth of our brains extends into the teenage years, and even beyond.

According to Dr. Frances Jensen, the 7 teenage years may be the most important period in the growth and development of the human brain. This period of neural development is the likely culprit for a teenager’s moody and irrational behaviour. It may also be the reason why so many mental illnesses start to show up in adolescence.

One of the brain structures that is still developing in teenagers is the frontal cortex. The frontal cortex is also responsible for important cognitive processes like reasoning and judgement. In fact, this area of the brain doesn’t fully develop until the mid-20s or 30. This might explain why your honours student child feels the need to text and drive. Or even experiment with recreational drugs.

The neural connections between the frontal cortex and other parts of the brain are also in their infancy. These connections are colloquially known as the white matter of the brain.

The white matter isn’t actually fully developed until we are in our 20s. In conjunction with this wiring, the teenage brain is also undergoing a process known as myelination.

Myelination is the process by which these growing wires are coated in a substance known as myelin. In keeping with the electrical analogy, myelin acts as the insulator to the wire that is carrying the electricity. Myelin helps increase the speed by which these neuronal signals travel throughout the brain.

So, teenagers’ brains are not yet fully connected. And when they are, they can’t send signals as efficiently as a fully-developed adult brain. But, what does this all mean?

Without the capability to effectively activate and recruit their pre-frontal cortex (the cognitive centre), teenagers have a biologically reduced ability to make sound judgments. And so they engage in rash and impulsive behaviour.

The Role of Hormones

As we all know, the secretion of hormones runs rampant throughout the teenage years. These hormones show their effect in the brain’s emotional centre: the limbic system.

An undeveloped prefrontal cortex, reduced communication, and an increase in emotional chemicals result in the perfect storm for teenager behaviour.

Research also shows that certain hormones have different effects on adults and teenagers. The chemical may have a calming effect in one age group, but an excitatory effect on the other. Hormones can also have an effect on the brain’s circuitry system (remember the myelination?).

Scientific evidence shows when hormones like testosterone and estrogen migrate to the brain, they actually stimulate the growth of new axons (the wiring). Increasing evidence also shows that these same hormones may actually be responsible for the myelination process.

Testosterone and estrogen don’t just form new connections, they actually delete the unnecessary ones. This occurs in a process known as synaptic pruning. Dr. Jensen believes that synaptic pruning is necessary for proper adolescent brain development. Throughout the teenage years, weaker neuronal connections are removed. And stronger ones are strengthened.


Dopamine is the molecule responsible for pleasure. Along with hormone production, the regulation of dopamine release also changes in a teenager’s brain. And so this change in regulation may also explain a teen’s erratic and impulsive behaviour.

The teen may recognize that a certain activity is risky. But their brains are pre-wired to experience more pleasure after engaging in said activity. This is why so many teens engage in risky driving behaviours. And why they engage in alcohol, drug, and sexual experimentation.

Drugs and Alcohol

So, it’s well known that teens engage in risky substance abuse behaviours. Why is this the case?

The teen brains are in a continuous evolving stage. That’s why teens are also more susceptible to outside factors like drugs and alcohol.

For instance, the brain cells of teens are more susceptible to alcohol toxicity. To study this, researchers exposed rat brain cells to alcohol. And recorded the recovery capabilities of adult vs. teen cells.

They found that once they removed alcohol, the adult cells easily recovered. But the teenage cells remained incapable of functioning in a proper way.

What about the hot topic of marijuana? People fall on both sides of the argument: marijuana does nothing to the teenage brain, or it has a profound impact on the brain. What does the science say?

According to a massive review conducted by the Globe and Mail, marijuana does have a significant impact on teenage brain health.

Marijuana may not be the most dangerous drug out there. But it does have a similar effect on the brain as alcohol. Research out of the University of Ottawa aimed to show how regular marijuana use could affect different areas of the brain. The results showed that regular marijuana use resulted in increased brain activity. Especially, in areas associated with attention and working memory.

When we hear of “increased activity” in the brain, we generally think of this as a good thing. But Dr. Andra Smith, the lead investigator, cautions against this assumption.

She states that the increased activity can be good in some cases. But in this case, it means that the brain is recruiting more neural resources and has to work harder.

Much like hormones do, marijuana can also have a profound structural effect. Researchers of Northwestern University found that those who regularly engaged in recreational marijuana use exhibited structural changes in the brain. The areas of the brain associated with emotion and reward regulation.

Marijuana does have some medical benefits. But users should be particularly sensitive to its effects on the teenage brain.

The Role of Sleep

Sleep-deprivation is seen at an alarming rate in adolescents. They wake up early for school. Stay in class for 8 hours a day. Go to their part-time job. Engage in social activity. Complete their homework. And then try to go to bed.

So teenagers aren’t getting enough sleep. As we all know, sleep is paramount to not only physical well-being but also our mental faculties. Without enough sleep, teenagers are curbing their ability to learn and remember new material.


Coupled with a lack of sleep and the hectic lifestyle of teenagers, it makes sense that stress has a profound effect on the adolescent brain.

Chronic stress can increase the size of the amygdala (the emotion centre). And reduce the size of the hippocampus (the brain’s memory centre).

This chronic stressful state leads to a brain that is hard-wired to have memory and learning problems. And a larger propensity for anxiety related disorders.


In this technologically advanced age, you always hear that too much electronic exposure can be bad for you. For teenagers, this couldn’t be more accurate.

According to Jensen, this overloading of our sensory system has a profound impact on learning and memory. One study, in particular found that sensory overloading actually reduced university students’ ability to recall words.

We often think of teenagers as emotional and irrational creatures. They can be impulsive, engage in emotional outbursts, and behave in ways that flabbergast adults. Parents ask themselves where they went wrong for their child to suddenly become so rebellious. “Is it my fault? Are they hanging around the wrong crowd?”

A proper upbringing is essential to proper behavioural development. But there is also a multitude of other factors at play.

As science shows us, the teenage brain is a fickle mystery of chemicals, hormones, and electrical activity. Unraveling the mysteries of the teenage brain is an exciting area of future research. And only by studying these factors in more depth, can we understand why teenagers act the way that they do.

What do you think? What other factors are at play here? Please add below in your comments.

Subscribe To Our Newsletter

Join our Weekly mailing list to get the most interesting Science News directly in your inbox!

You have Successfully Subscribed!