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October 1, 2015
Vol. 73
No. 2

Secrets of the Teenage Brain: A Conversation with Frances E. Jensen

The typical teen is a mystery to parents and teachers alike. Neuroscience yields some clues.

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As the mother of two teenage sons, Dr. Frances E. Jensen was puzzled when one of them wanted to dye his hair jet black with red streaks, and she was downright alarmed when the other totaled his car by trying to squeeze in a left turn in the path of oncoming traffic. As a neuroscientist, she wanted to find out why. In this interview with EL, she shares some of the insights she gained when she explored the neurological research, and she suggests how that research can help educators, parents, and teenagers themselves understand what's going on in the teenage brain.

Why is adolescence such an important time for brain development?

During the teenage years, our brains are both more powerful and more vulnerable than at any other time of our lives. They're powerful because teenagers and children have more synapses—connections between brain cells—than adults do. So teenagers are able to learn much more efficiently than adults, with less effort. That creates a huge opportunity—an optimal time window when teenagers can grow their cognitive strengths and work on their weaknesses.
As human beings, we start off with an excess of synapses, so as we get older, our brain prunes away the connections that we don't use. At the same time, as we have experiences, learn new information, or work on motor tasks, we strengthen the connections that we do use. That pruning and building process, called synaptic plasticity, is much more vigorous in teenagers than in adults.

I can see why teenage brains are powerful; why are they vulnerable?

In the last decade, we've learned more about one important area of vulnerability through functional magnetic resonance imaging, or fMRI. This technology enables us to look at the brain in real time and observe what regions light up during specific thoughts or actions.
We know that different regions of teenagers' brains haven't yet built strong connections from side to side and from back to front. The different regions of the brain connect through axons, and for a signal to travel from one region of the brain to another is actually a very long trip compared to the distance a signal travels from one adjacent brain cell to another.
Through functional MRI, we can see whether brain regions activate one another when teens engage in specific cognitive tasks—in other words, whether regions that "fire" together are "wired" together. A major study by the National Institutes of Health observed this activation in people through age 21 and found that the brain builds connectivity from the back to the front as we get older. The last region to build strong connectivity is the frontal lobe, and that isn't completed until early adulthood.
And what does the frontal lobe do? It's our seat of executive function, judgment, empathy, insight, and impulse control. One of the interesting challenges teenagers have is that they aren't able to access their frontal lobe for instant decision making the way that adults can. They have a frontal lobe—they use it when they take their SAT and in their physics class. But they can't necessarily access it when they're driving through an intersection and need to make a split-second decision to step on the brake, or when they need to decide whether to follow their impulse to click on that highly disturbing video online, or when they face a choice of whether to try that drug because their friends are telling them to.
Many studies have demonstrated the difficulty teenagers experience in accessing the frontal lobe. For example, researchers at Dartmouth College asked adolescents and adults to respond to questions about whether certain activities (such as swimming with sharks, setting your hair on fire, or jumping off the roof) were a good idea. The adolescents took more time than the adults to respond, and their responses activated a more limited brain region; they appeared to rely on their ability to "reason" an answer, whereas the adults seemed to rely on automatic mental images and a visceral response.
Another reason adolescence can be a vulnerable time is that the teenage brain is highly impressionable and excitable because it has so many synapses, and synapses grow by being excited and turned on. That means that good experiences leave their mark much more quickly—but so do bad experiences. The clinical research shows that binge drinking, substance abuse, and stress all tend to have a stronger effect on teenagers than on adults. Addiction is actually a form of synaptic plasticity. When a reward circuit gets repeated exposure to a drug, that circuit starts to build stronger synapses. So sadly, the teenager can become more strongly addicted than the adult and have a much harder time shedding that addiction later.
Frustrated parents and teachers often say, "What was he thinking? How could this really smart student do something so stupid?" Well, it's partly because teenagers' connections to their frontal cortices are still under construction. Understanding the biology behind what can be frustrating behavior might make us a little bit more patient. It's not that kids are trying to be incredibly annoying or reckless; they just haven't developed that decision-making capacity. Yet they're independent enough to be able to get themselves into very precarious situations. They can drive, they can go places without an adult—so they're potentially at risk.
This combination of excitable synapses and sluggish connection to their judgment centers in the frontal cortex, combined with hormones, makes adolescents highly emotional. The main area of our brain controlling emotion and sexual desire, the limbic system, is located behind the frontal lobe, so it builds strong connections earlier than the frontal lobe does. Teenagers' threshold for emotions being activated is low. For example, studies have shown that if you show people a series of faces with different emotions on them, the brains of children and adults have a less hyped-up response than those of adolescents. And because teenagers also lack the emotion-regulating function of a strong frontal-lobe connection, emotions are potentially going to drive behavior more during the teen years than at any other time in life.

If heightened emotion and lack of impulse control are normal parts of being an adolescent, how can educators identify adolescents who might actually be having serious mental issues or emotional problems?

An interesting thing for educators to know is that some mental illnesses, like schizophrenia, bipolar disorder, and depression, tend to blossom in the mid to late teens and early 20s. Surprisingly, in many cases we need to have a mature enough brain to "do" mental illness. These mood and affective disorders involve abnormal functioning of the frontal lobes, and if the frontal lobes aren't strongly hooked up to the rest of your brain yet, you're unlikely to manifest adultlike schizophrenia. You may have a gene or a trait that is going to cause one of these diseases, but as a child you appear completely normal.
As far as realizing that a kid is having trouble, that's becoming increasingly hard with social networking and the sort of social isolation that the Internet is creating in our lives. Even normal kids may appear to be quite socially isolated. Parents may not be interacting with their children as much as they did a couple of decades ago. The kids are coming home from school, closing the door, and staying in their room all night. Often, teachers spend more time with the kids than their parents do, so I think that teachers may need to be more vigilant these days for warning signs.
If there's an extreme loss or gain of weight, if the child appears disheveled or is suddenly sleeping a lot in school, if they appear to be abusing substances, these are all warning signs that you're dealing with something more than just a moody teenager who's just broken up with his or her girlfriend or boyfriend.
Anxiety and related disorders like anorexia, obsessive-compulsive disorder, panic disorder, and other social phobias are prevalent in this age window. In fact, recent reports have identified an epidemic of anxiety in teens. We should take note if we see a teenage withdraw from daily activities and become hesitant to engage in new experiences. Or they may go in the opposite direction and engage in more risk taking, such as drug experimentation, as a way to deny their fears. They may also experience physical symptoms like headaches, stomachaches, fatigue, or hyperventilation.

What are the likely sources of that epidemic of anxiety, and how does it physically manifest itself in the brain?

Our teenagers' lives are very intense these days. I blame the Internet partly for that. Social media can be a source of stress that can push young people over the edge. I also blame our hypercompetitive culture, in which parents are made to believe they're being neglectful if they don't have their child in several after-school activities and talent-building classes at the end of the day, not recognizing that kids need some down time.
I think sleep deprivation plays a role. Sleep is crucial to mental health—especially for teens, whose brains are so active. Teenagers' biological clocks are typically geared to fall asleep late and get up late. For one thing, melatonin, a hormone needed to induce sleep, is released two hours later in average teenagers than in average adults, so they don't even get sleepy until around midnight. When we wake them up at 6:00 a.m., it's like waking an adult up at 3:00 or 4:00 in the morning. That's not great for learning, and it's certainly not great for anxiety and stress.
Studies have shown that stress during the teenage years can have long-lasting effects. Even though a teen may be adult-size, his or her brain is not adult yet. It's still building itself. Every day, it's building something. So whether it's chronic pot smoking, binge-drinking episodes, or stress, any negative experiences can stall brain development. And you can't ever get that development opportunity back. That's why this is such a sensitive time.

Can giving adolescents the facts about what's going on with their brains help them deal with these emotions and stress? What role can schools play in giving them that information?

This generation of young people actually has a fair amount of respect for data and information. They grew up in the information age, and they're data-driven. So I believe that you can give them power by giving them facts.
They are also fascinated with themselves at this point. And they should be. Adolescence is a time for figuring out your identity and who you're going to be for the rest of your life. They're very interested in why they do the things they do—and they're often just as puzzled as the adults are.
It comes as a relief to them to know that there's biology behind their behavior. And it certainly comes as a relief to parents and teachers. Over and over, when I've presented this information, parents and teachers will say, "Oh, so that's why! I can't really do much about it, but it helps to know why this teenager is acting this way." People shouldn't be beating themselves up that they didn't know much about how the teenage brain works; a lot of this research is only five years old. It needs to get out of the ivory-tower journals and into people's lives.
I wish that every teenager had to take a course on how their brain works so that they would understand that they're building their brain by what they do every day. One discovery in the field, for instance, is that your IQ can change during your teen years. We all thought that IQ was an innate property—that you could discover what your IQ is in grade school with tests, and that's the IQ you're stuck with. Well, big surprise—no. In a third of people the IQ stays the same, but in a third it goes up, and in a third it goes down. A lot of young people may not start off looking like scholars, but during the teen years they might actually turn into scholars. That's not only hugely important for educators to know, but it's also a powerful piece of information for kids to have.
Being educated about the brain would allow teenagers to understand some of their behaviors and to realize that there's an opportunity to continue to change in a positive way. Even if a teenager does something like shoplifting, that doesn't mean that that's who they're fated to become. They don't need to pigeonhole themselves; they could be totally different people in another six years. That's a hopeful message for teenagers.
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