Neuroscience of the Teenage Brain – The Changes of Adolescence

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What is Adolescence?

Although we often use the words adolescent and teenager interchangeably, they actually refer to different things. A teenager is a young person between the ages of 13 and 19, while the start of adolescence is marked by the onset of puberty, and its end is generally accepted to be around the age of 19 or 20. While teenagerhood is a social idea, adolescence is a period of biological development common to all human cultures, and one that is also found in many non-human species.

During adolescence young people begin to pull away from their parents and to assert their independence and individuality. At the same time they start to explore their identity and how they fit in with their peers as well as society as a whole. The opinion of their peers is likely to matter more to an adolescent than that of their parents or other adults. They may behave more impulsively and take more risks than before without thought of the consequences, while their sleep patterns change drastically. You’ll be relieved to hear that there are reasons for all this! Our science editor Samantha Gouldson investigates the neuroscience of the teenage brain.

What Causes the Changes?

The onset of puberty and adolescence triggers many noticeable physical changes; these include growth spurts and the development of adult sexual characteristics such as breasts, menstruation, facial hair and body hair. But there are also a lot of changes happening that we can’t see, and these are arguably the most important. These changes are happening in the brain, and are believed to be responsible for the adolescent’s altered behaviour.

What Happens in a Adolescent Brain?

First of all we need to talk about grey matter. Put simply, grey matter is the part of the brain that we think with; it is responsible for our sensory perceptions, emotions, decision-making, self-control and speech. It’s made up of nerve fibres, neurons (the brain’s cells) and synapses (the connections between those cells, also known as the basic circuitry of our brains). To give you an idea of how incredibly complex our brains are, 1 cubic millimetre of grey matter can contain 35-70 million neurons and up to 500 billion synapses.

It used to be thought that grey matter peaked in early childhood and gradually declined from then on, but years of research have shown differently. Neuroscientists now know that in fact our brains have the most grey matter in late childhood and early adolescence; after this it declines until somewhere during our twenties, when it plateaus until old age. A person’s capacity to learn is never greater than in adolescence because this is when the brain has its greatest plasticity; its ability to re-organise itself.

How Does Grey Matter Change During Adolescence?

The reason that grey matter peaks in early adolescence is because from then until our twenties our synapses are being re-organised and the excess removed. Imagine the brain as a particularly spongy sort of rosebush; the strong shoots are left to grow and blossom, while the weak and damaged shoots are pruned away. This is what’s happening in the adolescent brain. The synapses that are used most become strengthened, whereas those that are used minimally are removed. During adolescence approximately 17% of the peak-level synapses vanish.

Remember that grey matter is responsible for our emotions as well as our self-control and decision-making? The environment that an adolescent is exposed to can actually change the way their brain works, thanks to this synaptic pruning. A happy, supported and enthusiastic adolescent will be reinforcing these positive pathways in the brain. Because of this, trauma suffered in childhood and adolescence can have a subtle but significant effect on the brain. While our brains retain their base state of neuroplasticity, so that later interventions can be beneficial, environment is key to the development of a healthy adolescent brain.

Why do Adolescents Love Risk?

The propensity of the adolescent to indulge in risky behaviour has its basis in societal influences as well as biological ones. Over and over again research has shown that adolescents will change behaviour when they’re being observed by their peers, or think they are. This isn’t unique to humans; studies of adolescent rats and mice have found that they consume more alcohol when their peers are present than when they’re alone!

Although boys are widely assumed to take more risks than girls, in fact they’re just different. Boys tend to take risks which could result in physical harm, whereas girls are more likely to take risks that could result in social harm. Gossiping (a stereotypically female trait) is as much a high-risk behaviour as leaping from heights or fighting (stereotypically behaviours demonstrated by the adolescent male).

In evolutionary terms, adolescent risk-taking has the benefit of establishing social status as well as impressing potential mates, but that’s not the sole reason for the risky behaviour we often see in adolescence. Some studies have found that parts of the brain develop at a different rate to others; namely the prefrontal cortex and the limbic system.

The prefrontal cortex is the front part of the brain and is responsible for planning, problem-solving, decision-making, self-awareness and the inhibition of inappropriate actions (among other things!). In contrast, the limbic system is buried deep within the brain and is responsible for emotions and rewards such as the release of ‘happy hormones’ such as seratonin. I like to think of them as the sensible angel and mischievous devil on your shoulder that are so beloved by cartoonists!

There is some evidence to suggest that in adolescents, the limbic system develops before the prefrontal cortex. In other words, the devil is stronger than the angel; for much of adolescence the urge to feel the rush or ‘kick’ that results from risky behaviour is stronger than the self-control and inhibitive aspects of the prefrontal cortex.

Why do Adolescents Sleep So Much?

The stereotype of the adolescent that sleeps until late in the day is common for a reason, and it has nothing to do with laziness. The circadian rhythms that determine when we feel tired and when we wake up actually change once puberty has begun. A younger child’s body produces melatonin, a hormone that helps us to sleep, during early evening. An adolescent’s circadian rhythms shift so that melatonin isn’t produced until significantly later at night; this means that deep sleep is harder to come by until the night is partly over and so the individual needs to sleep later in the day.

If there’s anything that adolescent neuroscience tells us, it’s that adolescence is a lot more complex than the stereotypes would have us believe. While there are many common traits, and studies have shown many common causes for stereotypical behaviour, each adolescent is an individual and there will be significant differences between them.


Further Information



 Blame My Brain: the Amazing Teenage Brain Revealed by Nicola Morgan

Nicola Morgan’s carefully researched, accessible and humorous examination of the ups and downs of the teenage brain has chapters dealing with powerful emotions, the need for more sleep, the urge to take risks, the difference between genders and the reasons behind addiction or depression.

Parenting the Teenage Brain: Understanding a Work in Progress by Sheryl Feinstein

The field of neuroscience is continually churning out exciting discoveries that help us better understand the human brain. Observing the brain while in action provides rich information on the behavior of teenagers giving us insight into their emotional and cognitive state. This book combines research from neuroscience and psychology along with a heavy dose of common sense and humor to offer parents important strategies to support and guide their teenager.

The Letter Your Teenager Can’t Write to You by Gretchen Schmelzer

A moving and emotional blog post

“This fight we are in right now. I need it. I need this fight. I can’t tell you this because I don’t have the language for it and it wouldn’t make sense anyway. But I need this fight. Badly. I need to hate you right now and I need you to survive it. I need you to survive my hating you and you hating me. I need this fight even though I hate it too. It doesn’t matter what this fight is even about: curfew, homework, laundry, my messy room, going out, staying in, leaving, not leaving, boyfriend, girlfriend, no friends, bad friends. It doesn’t matter. I need to fight you on it and I need you to fight me back”. 

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