Being a teenager is hard, and so is living with one, I'm told. No human gets to escape this moody, angsty, confusing phase and interestingly, such an extended adolescence is unique to humans. Other animals grow up a lot faster than we do. And you may think our teen years are just about streamlining bodes for baby making, but as it turns out, the storms of sex hormones that we associate with the teenage years are only a small part of what's really going on in the teenage body. Most of the action, it turns out, is happening in the brain.

Until fairly recently, we thought that the brain finished the nuts and bolts of its development by the time we started kindergarten, but really, right as puberty rolls in, it undergoes massive remodeling. This amounts to several years of neural growing pains as well as the other, more visible growth that's going on all over your body.

So take heart, whether you're going through it now, or about to go through it, or you count yourself among the veterans of that turbulent decade, know that the result of the teen years is a stronger, faster, more sophisticated brain. I wish someone had told me that twenty years ago.

(Intro)

Let's start with that obvious scapegoat of adolescent anguish: hormones. That word itself is kind of a lazy short hand that people use to describe the chemicals that some of our glands excrete that can affect our behavior. But the fact is, hormones have all kind of jobs that have nothing to do with where you grow hair, or what turns you on, or whether you feel glum for no apparent reason. Hormones keep your heart beating and your body hydrated and they make your organs grow and make you grow bone and muscle and skin.

What people actually mean when they talk about "teenage hormones" are sex hormones. And yes puberty involves a whole series of sex hormone storms, the first of which actually kicks in before you're out of primary school. That's when the adrenal glands start secreting androgens which trigger the growth and activity of the skin's sebaceous glands, making skin more oily. Soon enough, more apocrine, or sweat glands get activated, increasing body odor. Then comes the wave of hormonal agents that start activating the gonads. For boys this influx of luteinizing hormones from the pituitary gland get testosterone brewing in the testes, and suddenly that guy has up to fifty times more testosterone than he did before puberty. This also changes the shape of the male body, promoting hair growth and building up lean muscle mass, just as the increased presence of estrogen in girls rearranges the deposition of their fat, stimulating the growth of breasts.

Humans are actually lucky to experience the craziness of puberty only once, many other animals undergo multiple, similarly intense hormonal rodeos as they enter sexually active periods, sometimes called "the rut" or "heat" every new breeding season. Some male species completely stop eating during their breeding period because they're just that sex crazed.

And yet, all that said, teens are far less ruled in their hormones than you might think. There are other factors that play here. For example, your favorite moody teen may be by terms, punchy, angry, depressed, or in a zombie like fog because of their chronic lack of sleep.

Sleep is vital to everyone, but it's especially important for kids and teens because it's during sleep that your pituitary gland releases an essential growth hormone necessary for development. A normal sleep cycle driven by circadian rhythm is regulated by the daytime release of cortisol, which helps you wake up, and melatonin, which helps you wind down when it gets dark.

But this biology of sleep timing changes as we age, and as puberty begins, teens' sleep clocks get pushed back. Most adults start oozing melatonin at about 10:00pm-ish, but one study showed that teenagers don't start producing melatonin until closer to 1:00am. This may be because puberty's hormonal frenzy is stalling the release of melatonin, and could partly explain why so many teens stay up late, energized by the night, but have a really hard time rolling out of bed with the alarm. Of course it's a bit of a chicken and egg deal since watching reruns of The Simpsons and playing Call of Duty late into the night continues to stimulate the brain, which may further delay the release of melatonin. Still, some researchers are starting to advocate pushing back high school start times in the morning in the hopes of having more focused students.

So we got sex hormones changing the body and a lack of sleep to contend with, but increasing evidence suggests that there is something much bigger at work that is making teenagers so…teenagery: their brains.

It turns out that brains actually take longer than we thought to fully mature. I don't mean physical size -our brains are already about 95% full-sized by the time we're just six- but more in the sense of the connections inside the brain. Adults, for the most part, know how to make decisions by evaluating choices and weighing consequences. They do this with their prefrontal cortex, which is responsible for controlling impulses and emotions and forming judgments. Its neurons chat with the neurons in other regions of the brain responsible for, say, memory or movement through synapses.

Thing is, teenage brains don't quite work like this yet. The prefrontal cortex may not be fully developed until your mid-twenties, and teen synapses, those lines of communication are still growing and specializing. They're also slow.

As an adolescent brain keeps developing, its axons, the long, tail-like parts of the neurons that transmit signals to other neurons, become more and more insulated by a fatty layer called the myelin sheath. This padding greatly increases the cell's transmission speed, and while it helps adults make fast decisions, it isn't fully formed in teens.

These changes occur slowly, beginning at the back of the brain where the oldest and most fundamental brain parts reside, and slowly working its way forward to the more advanced and complicated brain bits. The prefrontal cortex is the last to be hooked up and shaped. So it's important to keep in mind that just because your favorite teenager stayed up until sunrise, binge watching The Walking Dead the night before an exam, it doesn't mean they're dumb or lazy. Their brains are just literally finishing being built.

But at the same time, because all this brain building is just starting to peak, this is also when the brain starts getting thinned out. You actually start losing connections that you don't use enough in a process called 'synaptic pruning', which has led to a theory that this is kind of a 'use it or lose it' phase, meaning adolescence could be an especially important time to use your brain. Play an instrument, engage in sport, write poetry, learn a language! Because by doing these things you're helping hard-wire those synapses and giving your brain topiary a lovely lasting shape. Whereas if you're sitting around all day playing Candy Crush, those will be the connections that survive. Which you don't need.

This shaping of the teen brain manifests itself in other ways too, like in teenage attitudes. A group of scientists at the McLean Hospital in Massachusetts once hooked up a group of adults and a group of teens to MRI devices and then asked them to identify a series of expressions on photographs of adult faces. Interestingly, while adults correctly identified one expression as fear, the teenagers thought the faces showed anger, surprise, or shock. They weren't registering subtlety as well. Not only that, but the MRI images showed that adults and teens responded with different parts of their brains. Adults used the reasonable prefrontal cortex, while the teens mostly used the 'gut reaction' emotional amygdala located farther back in the brain.

Results like these might help explain why teenagers seem to experience frequent mood swings. For one, they tend to react quickly from the emotional part of their brain without running those reactions by the more rational frontal cortex, and two, it could be that they're just misreading expressions and therefore the intentions behind them.

The frontal cortex also helps people relate to and understand each other, and you can imagine what happens when concern is misjudged as anger, or worry as disappointment. The Fresh Prince has an entire song about it. But the truth is, as much as parents just don't understand, teens don't always understand either. When the emotional amygdala and the more rational cortex aren't fully hooked up yet, that can make it hard for teenagers to productively work through emotions. 

This kind of reactionary impulse behavior may also lead to more risk-taking. Adolescence is the time when we're most likely to experiment with whatever booze, drugs, or toad licking is available, and unfortunately it's also the time our developing brains are most vulnerable to lasting effects. Studies have shown that teens are more likely to become addicted to drugs and alcohol than adults, partly because their brains are more attuned to their reward centers.

While the teen prefrontal cortex is still developing their nucleus accumbens, or pleasure and reward zone, forms early on. Neuroimaging studies have shown that, when presented with a big potential reward, teen brains light up way more than kid or adult brains. But if the reward was small teenage brains hardly fired at all. So basically, give an adolescent a pat on the back and you'll get a shrug. Give them a hot date or a winning goal, and their brains light up like Vegas.

This, of course, does not always result in great judgment. A jacked-up thrill-seeking impulse combined with an exquisite pang of peer pressure plus a new driver's license, new sex parts, and access to substances, can lead to some not-good results.

But still, this long and sometimes tedious remodelling process that our bodies go through in the teenage years isn't all that. Many scientists have pointed out that our delayed adolescence lets our brains keep their flexibility longer which, yeah, may make teens a little slow, but also more adaptable as they prepare for the adult world. In this way, you can see teen impulsiveness as boldness or independent thinking, and moodiness as a source of newfound empathy, and excitability as passion. Which means there's a lot of awesome energy floating around out there, ready to decrease all kinds of world suck.

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