Kitabı oku: «The Teenage Brain: A neuroscientist’s survival guide to raising adolescents and young adults»

Contents

Cover

Title Page

Copyright

Dedication

Epigraph

List of Illustrations

Introduction: Being Teen

1 Entering the Teen Years

2 Building a Brain

3 Under the Microscope

4 Learning: A Job for the Teen Brain

5 Sleep

6 Taking Risks

7 Tobacco

8 Alcohol

9 Pot

10 Hard-Core Drugs

11 Stress

12 Mental Illness

13 The Digital Invasion of the Teenage Brain

14 Gender Matters

15 Sports and Concussions

16 Crime and Punishment

17 Beyond Adolescence: It’s Not Over Yet

Postscript: Final Thoughts

Glossary

Notes

Selected Bibliography

Resources

List of Seacrhable Terms

Acknowledgements

About the Authors

Also by Amy Ellis Nutt

About the Publisher

Illustrations

Introduction Being Teen

What was he thinking?

My beautiful, auburn-haired son had just returned home from a friend’s house with his hair dyed jet-black. Despite my inward panic, I said nothing.

“I want to get red streaks in it,” he told me nonchalantly.

I was gob-smacked. Is this really my child!? I’d begun to ask the question often during my fifteen-year-old son Andrew’s sophomore year at a private high school in Massachusetts, all the while trying to be empathetic. I was a divorced working mother of two teenage sons, putting in long hours as a clinician and professor at Boston Children’s Hospital and Harvard Medical School. So if I sometimes felt guilty about the time I spent away from my boys, I also was determined to be the best mother I could be. After all, I was a faculty member in a pediatric neurology department and actively researching brain development. Kids’ brains were my business.

But my sweet-natured firstborn son had suddenly become unfamiliar, unpredictable, and bent on being different. He had just transferred from a very conventional middle school that went through ninth grade, where jackets and ties were the norm, to a very progressive high school. Upon arriving, he took full advantage of the new environment, and part of that was to dress in what you might describe as an “alternative” style. Let’s face it, his best friend had spiky blue hair. Need I say more?

I took a deep breath and tried to calm myself. Getting mad at him, I knew, wouldn’t do either of us any good and probably would only alienate him further. At least he felt comfortable enough to tell me about something he wanted to do before he actually did it. This was an opportunity, I realized, and I quickly seized it.

Instead of damaging your hair with some cheap, over-the-counter dye, what if I take you to my hair guy for the red streaks? I asked him. Since I also was going to pay for it, Andrew happily agreed. My hair stylist, who was a sort of punk rocker himself, got totally into the task. He did a great job, actually—so good that Andrew’s girlfriend at the time was inspired to color her hair in exactly the same black-and-red motif. She attempted this herself, and needless to say had different results.

Thinking back to those days, I realize so much of what I thought I knew about my son during this turbulent time of his life seemed turned on its head. (Was that a compost pile in the middle of his bedroom, or laundry?) Andrew seemed trapped somewhere between childhood and adulthood, still in the grip of confusing emotions and impulsive behavior, but physically and intellectually more man than boy. He was experimenting with his identity, and the most basic element of his identity was his appearance. As his mother and a neurologist, I thought I knew everything there was to know about what was going on inside my teenager’s head. Clearly I did not. I certainly didn’t know what was going on outside his head either! So as a mother and a scientist, I decided I needed to—I had to—find out.

Professionally, I was primarily studying the brains of babies at that time and running a research lab largely devoted to epilepsy and brain development. I was also doing translational neuroscience, which means, simply, trying to create new treatments for brain disorders. Suddenly, however, I had a new scientific experiment and project: my sons. My younger son, Will, was just two years Andrew’s junior. What would I be in for when Will reached the same age as his older brother? There was so much I didn’t get. I had watched Andrew, almost overnight, morph into a different being, yet I knew, deep inside, he was still the same wonderful, kind, bright kid he’d always been. So what happened? To figure it out I decided to delve into the world of research on this somewhat foreign species in my household called the teenager, and use that knowledge to help me and my sons navigate their way more smoothly into adulthood.

The teen brain has been a relatively neglected area of study until only the past decade. Most research dollars in neurology and neuropsychology are spent on infant and child development—from learning disabilities to early enrichment therapy—or, at the other end of the spectrum, on diseases of the elderly brain, especially Alzheimer’s. Up until just a few years ago, the neuroscience of the adolescent brain was underfunded, underresearched, and obviously not well understood. Scientists believed—incorrectly, as it turned out—that brain growth was pretty much complete by the time a child started kindergarten; this is why for the past two decades parents of infants and toddlers, trying to get a jump on their children’s education, have inundated their kids with learning tools and accessories like Baby Einstein DVDs and Baby Mozart Discovery Kits. But the adolescent brain? Most people thought it was pretty much like an adult’s, only with fewer miles on it.

The problem with this assumption is that it was wrong. Very wrong. There are other misconceptions and myths about the teenage brain and teenage behavior that are now so ingrained they are accepted societal beliefs: teens are impulsive and emotional because of surging hormones; teens are rebellious and oppositional because they want to be difficult and different; and if teenagers occasionally drink too much alcohol without their parents’ consent, well, their brains are resilient, so they’ll certainly rebound without suffering any permanent effects. Another assumption is that the die is cast at puberty: whatever your IQ or apparent talents may be (a math or science type versus a language arts type), you stay that way for the rest of your life.

Again, all wrong. The teen brain is at a very special point in development. As this book will reveal, I learned that there are unique vulnerabilities of this age window, but there is also the ability to harness exceptional strengths that fade as we enter into adulthood.

The more I studied the emerging scientific literature on adolescents, the more I understood how mistaken it was to look at the teenage brain through the prism of adult neurobiology. Functioning, wiring, capacity—all are different in adolescents, I learned. I was also aware that this new science of the teenage brain wasn’t reaching most parents, or at least wasn’t reaching parents who don’t have a background in neuroscience as I did. And this was just the audience who needed to know about this new science of the adolescent brain: parents and guardians and educators who are just as perplexed, frustrated, and maddened by the teenagers in their care as I was.

When my younger son, Will, was sixteen, he passed his driver’s test. He’d rarely given me cause to worry, but that changed early one morning. A few weeks after getting his license, he had started to drive himself to school in our 1994 Dodge Intrepid—a big, old, safe car. All seemed to go well. As usual, Will left around 7:30, as school started at 7:55. Off he went. Just as I was walking out the door to go to my job, at about 7:45, I got a call from Will: “Mom, I’m okay, but the car is totaled.” Well, first, I was thankful he had the presence of mind to lead off with telling me he was okay, but I had visions of his car wrapped around a tree. I said, “I’m on my way,” and jumped in my car. As I was approaching the school entrance, I saw the flashing lights of the police cars. What had he done? Well, simply put, he had decided that he could squeeze a left turn into the school entrance in the path of rapidly moving traffic going in the opposite direction. This might have worked if there had been another mother like me driving in the opposite direction who would have shaken her head and slammed on her brakes. But in Will’s case that morning, it was a twenty-three-year-old guy, a construction worker in a Ford F-150 on his way to work. He was no more in the mood to give the right-of-way than Will had been to wait to cross the road. So—the accident happened. It was good to know that 1994 airbags still worked in 2006.

There was Will standing by his completely trashed car at the very entrance of his school, looking sheepish as basically the entire school drove by him as students and staff arrived for the day. What a lesson for Will. I recognized that immediately—and was so thankful that he and the other driver had emerged unscathed from this battle of wills as to who had the right-of-way.

What was he thinking? I asked myself, almost reflexively.

Then: Oh, no, here we go again.

This time, however, I quickly calmed myself. I knew a lot more now. I knew Will’s brain, like Andrew’s, like every other teenager’s, was a work in progress. He clearly was no longer a child, and yet his brain was still developing, changing, even growing. I hadn’t recognized that until Andrew made me sit up and take stock of what I knew about the pediatric brain, that it’s not so much what is happening inside the head of an adolescent as what is not.

The teenage brain is a wondrous organ, capable of titanic stimulation and stunning feats of learning, as you will learn in this book. Granville Stanley Hall, the founder of the child study movement, wrote in 1904 about the exuberance of adolescence:

These years are the best decade of life. No age is so responsive to all the best and wisest adult endeavor. In no psychic soil, too, does seed, bad as well as good, strike such deep root, grow so rankly or bear fruit so quickly or so surely.

Hall said optimistically of adolescence that it was “the birthday of the imagination,” but he also knew this age of exhilaration has dangers, including impulsivity, risk-taking, mood swings, lack of insight, and poor judgment. What he couldn’t possibly have anticipated back then is the breathtaking range of dangers teens would be exposed to today through social media and the Internet. How many times have I heard from friends, colleagues, even strangers who have reached out to me after hearing me speak, about the crazy things their teenage kids or their friends just did? The daughter who “stole” her father’s motorcycle and crashed it into a curb. The kids who went “planking”—lying facedown, like a board, on any and every surface (including balcony railings), and then taking photos of one another doing it. Or worse: “vodka eyeballing,” pouring liquor directly into the eye to get an immediate high, or, scared about passing a drug test for a weekend job, ingesting watered-down bleach, thinking it would “clean” their urine of the pot they had smoked the night before.

Children’s brains continue to be molded by their environment, physiologically, well past their midtwenties. So in addition to being a time of great promise, adolescence is also a time of unique hazards. Every day, as I will show you, scientists are uncovering ways in which the adolescent brain works and responds to the world differently from the brain of either a child or an adult. And the way that the adolescent brain responds to the world has a lot to do with the impulsive, irrational, and wrongheaded decisions teens seem to make so frequently.

Part of the problem in truly understanding our teenagers lies with us, the adults. Too often we send them mixed messages. We assume that when our kid begins to physically look like an adult—she develops breasts; he has facial hair—then our teenager should act like, and be treated as, an adult with all the adult responsibilities we assign to our own peers. Teenagers can join the military and go to war, marry without the consent of their parents, and in some places hold political office. In recent years, at least seven teens have been elected mayors of small towns in New York, Pennsylvania, Iowa, Michigan, and Oregon. Certainly the law often treats teens as adults, especially when those teens are accused of violent crimes and then tried in adult criminal courts. But in myriad ways we also treat our teens like children, or at least like less than fully competent adults.

How do we make sense of our own conflicting messages? Can we make sense?

For the past few years I’ve given talks all over the country—to parents, teens, doctors, researchers, and psychotherapists—explaining the risks and rewards that pertain to the new science of the adolescent brain. This book was prompted by the tremendous, even overwhelming, number of responses I have received from parents and educators (and sometimes even teens) who heard me speak. All of them wanted to share their own stories, ask questions, and try to understand how to help their kids—and, in the process, themselves—navigate this thrilling but perplexing stage of life.

The truth of the matter is, I learned from my own sons that adolescents are not, in fact, an alien species, but just a misunderstood one. Yes, they are different, but there are important physiological and neurological reasons for those differences. In this book I will explain how the teen brain offers major advantages on the one hand but unperceived and often unacknowledged vulnerabilities on the other. I am hoping you will use this as a handbook, a kind of user’s manual or survival guide to the care and feeding of the teenage brain. Ultimately, I want to do more than help adults better understand their teenagers. I want to offer practical advice so that parents can help their teenagers, too. Adolescents aren’t the only ones who must navigate this exciting but treacherous period of life. Parents, guardians, and educators must, too. I have—twice. It is humbling, exhilarating, confusing, all at the same time. As parents, we brace ourselves for what will be quite a roller-coaster ride, but in the vast majority of cases the ride slows down, evens out, and gives one a lot of stories to tell afterward!

Nearly a decade ago, when it became clear to me that being a parent of teenagers was nothing like taking care of overgrown children, I said, Okay, let’s work on it together. I stayed in my sons’ faces. I remember one time, when Andrew was still a sophomore in high school, the inevitable point arrived when exams were just around the corner and he was still paying more attention to sports and parties than books and homework. Because I’m a scientist, I know learning is cumulative—everything new is based on something you just learned, so you have to hang in there, you have to stay on top of it. So I got a pad of paper and I went through each chapter of Andrew’s textbooks, and on one side of the paper I picked out a problem for him to solve and on the other side, folded, was the answer. All he needed was a model, a template, a structure. It was a turning point for him and me. He realized he actually had to do the work—sit down and do it—in order to learn. He also realized working on his bed, with everything spread out around him, wasn’t helping. He needed more structure, so he sat himself at his desk, with a pencil sharpener and a piece of paper in front of him, and he learned how to impose order on himself. He needed the external cues. I could plan and he couldn’t at that point. Having a structured environment helped him learn, and eventually he got really good at it, sitting in his chair at his desk for hours. I know because I’d check in on him. I also knew this was a good example of place-dependent learning. Scientists have shown that the best way to remember what you’ve learned is to return to the place where you learned it. For Andrew, that was his desk in his bedroom. As I will explain later, teenagers are “jacked up” on learning—their brains are primed for knowledge—so where and how they learn is important, and setting up a place where homework is done is something any parent can help teens do. And because homework is one of the main things kids do at home, you can stay involved with your teenagers even if you don’t happen to have an MD or PhD in the subject or subjects they’ve neglected for months. You can offer to proofread assignments, spell-check their essays, or simply make sure they are sitting in a comfortable desk chair. While you might not have the right hair guy to get red streaks, the point is that you can at least spring for a home hair dye when they want to transform themselves on the outside. Let them experiment with these more harmless things rather than have them rebel and get into much more serious trouble. Try not to focus on winning the battles when you should be winning the war—the endgame is to help get them through the necessary experimentation that they instinctively need without any longterm adverse effects. The teen years are a great time to test where a kid’s strengths are, and to even out weaknesses that need attention.

What you don’t want to do is ridicule, or be judgmental or disapproving or dismissive. Instead, you have to get inside your kid’s head. Kids all have something they’re struggling with that you can try to help. They can be all over the place: forgetting to bring their books home, crumpling important notes in the bottom of their backpacks, misconstruing homework assignments. Sometimes—or most of the time—they are just not organized, not paying attention to the details of what’s going on around them, and so expecting them to figure out how to do their homework can actually be expecting too much. Your teenagers won’t always accept your advice, but you can’t give it unless you’re there, unless you’re trying to understand how they’re learning. Know that they are just as puzzled by their unpredictable behavior and the uneven tool kit they call their brain. They just aren’t at a point where they will tell you this. Pride and image are big for teens, and they are not able to look into themselves and be self-critical.

That’s what this book is all about—knowing where their limits are and what you can do to support them. So that you won’t get angry or confused at your teens or simply throw your hands up in surrender, I want to help you understand what makes them so infuriating. Much of what is in this book will surprise you—surprise you because you probably thought teenagers’ recalcitrant behavior was something they could, or at least should, be able to control; that their insensitivity or anger or distracted attitude was entirely conscious; and that their refusal to hear what you suggest or request or demand they do was entirely willful. Again, none of these things are true.

The journey I will take you on in this book will actually shock you at times, but by the end of the journey I promise you will gain insight into what makes your teens tick because you’ll have a much better understanding of how their brains work. I make an effort in this book to reveal, wherever possible, the real data from real science journal articles. There is much data out there that has not been “translated” for the public. Even more important, the teen generation is one that holds information in great esteem. So when you talk to teens, you owe it to them to have actual data. I inserted as many figures into this book as I could where the actual science is shown, and I point out where it applies to our knowledge of the strengths and weaknesses of being a teen. There are lots of myths about teenagers out there that need to be debunked: this book is an attempt to chip away at those myths and explore the new science that is available to inform us.

For this book to be truly effective, however, you must remember a simple rule: First, count to ten. It became a kind of mantra for me when I was raising my sons. But it means more than just taking a deep breath. Let me explain. In leadership courses I’ve taken for my professional career, one theme that is always emphasized is the Boy Scouts’ motto, “Be prepared.” I learned in these seminars that the average time an American businessperson spends preparing for a meeting is about two minutes. We probably spend more time just scheduling those meetings than actually thinking about what we’re going to say or do in them. I don’t mean the big presentations. I mean the one-on-one encounters, which we too often step into cavalierly without taking much time for reflection beforehand. When I heard this statistic, initially it shocked me, but then I thought about my own professional world, where I am the head of a large university neurology department and have my own lab with many graduate and postgraduate students, and I realized, Yep, that’s pretty much what does happen. Not a lot of time is devoted to planning or “rehearsing” for all those one-on-one encounters with colleagues and staff, and yet it’s these more personal, more direct interactions that often play a pivotal role in the success of an organization. Similarly, the impression you give others in these encounters can affect the direction your career takes; this is why it’s so important to plan ahead, at least for more than just a few minutes, and think about how the other person will react during one of these meetings. In your mind, go through what you want to say, step by step, and imagine the range of responses. Now imagine that the other person is your teenage son or daughter. Being prepared for both positive and negative responses will help guide you as you consider your options about what to say or do next. If you appear hotheaded or mentally disorganized, you lose credibility, whether it’s with a colleague, an employee, or your teenager.

For parents or teachers, or anyone who has a caring relationship with a teenager, reading this book will arm you with facts—and with fortitude. Changing the behavior of your teen is partly up to you, so you have to come up with a plan of action and a style of action that fits your household and your kids, as well as your needs and wants. Remember, you are the adult, and if your child is under eighteen, you also are legally responsible for that “child.” Certainly the courts will hold you accountable for your child and, by extension, for the environment you provide for him or her. So take the lead, take control, and try to think for your teenage sons and daughters until their own brains are ready to take over the job. The most important part of the human brain—the place where actions are weighed, situations judged, and decisions made—is right behind the forehead, in the frontal lobes. This is the last part of the brain to develop, and that is why you need to be your teens’ frontal lobes until their brains are fully wired and hooked up and ready to go on their own.

But the most important advice I want to give you is to stay involved. As the mother of two sons I adore, I couldn’t physically maneuver them into doing what I wanted them to do when they were teenagers, not in the way I could when they were small children. Eventually they were simply too big to just pick up and put down where I wanted them to be. We lose physical control as children leave childhood. Our best tool as they enter and move through their adolescent years is our ability to advise and explain, and also to be good role models. If there’s anything I’ve learned with my boys, it’s that no matter how distracted or disorganized they seemed to be, no matter how many assignments they forgot to bring home from school, they were watching me, taking the measure of their mom as well as all the other adults around them. I will talk much more about this later in the book, but just so you know, it all turned out okay in my life and the lives of my sons. Here’s the bottom line on my two “former teenagers”: Andrew graduated from Wesleyan University with a combined MA-BA degree in quantum physics in May 2011 and is now in a joint MD-PhD program. Will graduated from Harvard in 2013 and landed a business-consulting job in New York City. So, yes, you can survive your teenagers’ adolescence. And so can they. And you will all have a lot of stories to tell after it’s all over.

1
Entering the Teen Years

In July 2010 I received an e-mail from the frustrated mother of a nineteen-year-old who had just finished his freshman year of college. The mother had heard me give a talk to parents and teachers in Concord, Massachusetts, about the teenage brain, and her e-mail expressed a wide range of emotions, from sadness to confusion to anger, about the boy, whose behavior had suddenly become downright “weird.”

“My son gets angry easily,” she wrote. “He puts a wall around him so he would not talk. He stays up all night and sleeps all day. He stops doing things he used to enjoy…. He was once charming, intelligent, outgoing. These days, good mood is rare. I thought I did all that hard work to raise him, to send him to a very good college, and it all ended up like this.”

The woman ended her e-mail with a simple question: “How do I help him?”

Letters and e-mails and calls like these are what prompted me to write this book. Nine months after that mother asked how she could help her son, I received a similar e-mail, this time from the mother of an eighteen-year-old girl. Her daughter, who had once seemed so levelheaded, she wrote, had let her grades slip in high school. She became defiant, ran away from home, and was hospitalized for depression. “This year has been difficult for us,” the mother wrote. “Sometimes it seems as if she has been replaced by an alien. It is because of the behavior and the things that she says. She is a completely different person.”

I knew how these women felt. At one time, I felt helpless, too. Because I was newly divorced as my older son, Andrew, entered adolescence, I was painfully aware that my children’s future, as well as their present, was largely up to me. There was no pulling my hair out and saying, “Go talk to your father about it!” When you’re a single parent, the buck stops with you. As parents, we want to open a few doors for our kids—that’s all, really. To gently nudge them in the right direction. During their childhood, everything seems to go pretty much by plan. Our kids learn what’s appropriate and what isn’t, when to go to bed and when to get up in the morning, what not to touch, where not to go. They learn the importance of school, of being polite to their elders, and when they are physically hurt or emotionally wounded, they come to us seeking solace.

So what happens when they reach fourteen, fifteen, or sixteen years old? How is it that the cute, even-tempered, happy, and well-behaved child you’ve known for more than a decade is suddenly someone you don’t know at all?

These are a few of things I say to parents right off the bat: The sense of whiplash you are feeling is not unusual. Your children are changing, and also trying to figure themselves out; their brains and bodies are undergoing extensive reorganization; and their apparent recklessness, rudeness, and cluelessness are not totally their fault! Almost all of this is neurologically, psychologically, and physiologically explainable. As a parent or educator, you need to remind yourself of this daily, often hourly!

Adolescence is a minefield, for sure. It is also a relatively recent “discovery.” The idea of adolescence as a general period of human development has been around for aeons, but as a discrete period between childhood and adulthood it can be traced back only as far as the middle of the twentieth century. In fact the word “teenager,” as a way of describing this distinct stage between the ages of thirteen and nineteen, first appeared in print, and only in passing, in a magazine article in April 1941.

Mostly for economic reasons, children were considered miniadults well into the nineteenth century. They were needed to sow the fields, milk the cows, and split the firewood. By the time of the American Revolution half the population of the new colonies was under the age of sixteen. If a girl was still single at eighteen, she was considered virtually unmarriageable. Well into the early twentieth century, children over the age of ten, and often children much younger, were capable of most kinds of work, either on the farm or later in city factories—even if they needed boxes to stand on. By 1900, with the Industrial Revolution in full swing, more than two million children were employed in the United States.

Two things in the decades spanning the middle of the twentieth century—the Great Depression and the rise of high schools—not only changed attitudes about the meaning of childhood but also helped to usher in the era of the teenager. With the onset of the Depression after the stock market crash of 1929, child laborers were the first to lose their jobs. The only other place for them was school, which is why by the end of the 1930s, and for the first time in the history of American education, most fourteen- to seventeen-year-olds were enrolled in high school. Even today, according to a 2003 survey by the National Opinion Research Center, Americans regard finishing high school as the number one hallmark of adulthood. (In much of the United Kingdom a teenager is treated as an adult even if he or she does not finish high school, and in England, Scotland, and Wales it is legal not only to leave school at age sixteen but to leave home and live independently as well.) In the 1940s and ’50s, American youth, most of whom were not responsible for the economic survival of their families, certainly did not seem like adults—at least not until they graduated from high school. They generally lived at home and were dependent on their parents, and as more and more children found themselves going to school beyond the eighth grade, they became a kind of class unto themselves. They looked different from adults, dressed differently, had different interests, even a different vocabulary. In short, they were a new culture. As one anonymous writer said at the time, “Young people became teenagers because we had nothing better for them to do.”

One man foresaw it all more than one hundred years ago. The American psychologist Granville Stanley Hall never used the word “teenager” in his groundbreaking 1904 book about youth culture, but it was clear from the title of his fourteen-hundred-page tome—Adolescence: Its Psychology and Its Relations to Physiology, Anthropology, Sociology, Sex, Crime, Religion and Education—that he regarded the time between childhood and adulthood as a discrete developmental stage. To Hall, who was the first American to earn a PhD in psychology, from Harvard University, and the first president of the American Psychological Association, adolescence was a peculiar time of life, a distinct and separate stage qualitatively different from either childhood or adulthood. Adulthood, he said, was akin to the fully evolved man of reason; childhood a time of savagery; and adolescence a period of wild exuberance, which he described as primitive, or “neo-atavistic,” and therefore only slightly more controlled than the absolute anarchy of childhood.

Hall’s suggestion to parents and educators: Adolescents shouldn’t be coddled but rather should be corralled, then indoctrinated with the ideals of public service, discipline, altruism, patriotism, and respect for authority. If Hall was somewhat provincial about how to treat adolescent storm and stress, he was nonetheless a pioneer in suggesting a biological connection between adolescence and puberty and even used language that presaged neuroscientists’ later understanding of the malleability of the brain, or “plasticity.” “Character and personality are taking form, but everything is plastic,” he wrote, referring to pliability, not the man-made product. “Self-feeling and ambition are increased, and every trait and faculty is liable to exaggeration and excess.”

Self-feeling, ambition, exaggeration, and excess—they all helped define “teenager” for the American public in the middle of the twentieth century. The teenager as a kind of cultural phenomenon took off in the post-World War II era—from teenyboppers and bobbysoxers to James Dean in Rebel Without a Cause and Holden Caulfield in The Catcher in the Rye. But while the age of adolescence became more defined and accepted, the demarcation between childhood and adulthood remained—and remains—slippery. As a society, we still carry the vestiges of our centuries-old confusion about when a person should be considered an adult. In most of the United States a person must be between fifteen and seventeen to drive; eighteen to vote, buy cigarettes, and join the military; twenty-one to drink alcohol; and twenty-five to rent a car. The minimum age to be a member of the House of Representatives is twenty-five; to be president of the United States, thirty-five; and the minimum age to be a governor ranges among states from no age restriction at all (six states) to a minimum age of thirty-one (Oklahoma). There is generally no minimum age requirement to testify in most courts, enter into a contract or sue, request emancipation from one’s parents, or seek alcohol or drug treatment. But you must be eighteen to determine your own medical care or write a legally binding will, and in at least thirty-five states those eighteen or younger must have some type of parental involvement before undergoing an abortion. What a lot of mixed messages we give these teenagers, who are not at a stage to weed through the logic (if there is any) behind how society holds them accountable. Very confusing.

So what does being a teenager mean? Man-child, woman-child, quasi-adult? The question is about much more than semantics, philosophy, or even psychology because the repercussions are both serious and practical for parents, educators, and doctors, as well as the criminal justice system, not to mention teens themselves.

Hall, for one, believed adolescence began with the initiation of puberty, and this is why he is considered the founder of the scientific study of adolescence. Although he had no empirical evidence for the connection, Hall knew that understanding the mental, emotional, and physical changes that happen in a child’s transition into adulthood could come only from an understanding of the biological mechanics of puberty.

One of the chief areas of focus in the study of puberty has long been “hormones,” but hormones have gotten a bad rap with parents and educators, who tend to blame them for everything that goes wrong with teenagers. I always thought the expression “raging hormones” made it seem as though these kids had taken a wicked potion or cocktail that made them act with wild disregard for anyone and anything. But we are truly blaming the messenger when we cite hormones as the culprit. Think about it: When your three-year-old has a temper tantrum, do you blame it on raging hormones? Of course not. We know, simply, that three-year-olds haven’t yet figured out how to control themselves.

In some ways, that’s true of teenagers as well. And when it comes to hormones, the most important thing to remember is that the teenage brain is “seeing” these hormones for the first time. Because of that, the brain hasn’t yet figured out how to modulate the body’s response to this new influx of chemicals. It’s a bit like taking that first (and hopefully last!) drag on a cigarette. When you inhale, your face flushes; you feel light-headed and maybe even a bit sick to your stomach.

Scientists now know that the main sex hormones—testosterone, estrogen, and progesterone—trigger physical changes in adolescents such as a deepening of the voice and the growth of facial hair in boys and the development of breasts and the beginning of menstruation in girls. These sex hormones are present in both sexes throughout childhood. With the onset of puberty, however, the concentrations of these chemicals change dramatically. In girls, estrogen and progesterone will fluctuate with the menstrual cycle. Because both hormones are linked to chemicals in the brain that control mood, a happy, laughing fourteen-year-old can have an emotional meltdown in the time it takes her to close her bedroom door. With boys, testosterone finds particularly friendly receptors in the amygdala, the structure in the brain that controls the fight-or-flight response—that is, aggression or fear. Before leaving adolescence behind, a boy can have thirty times as much testosterone in his body as he had before puberty began.

Sex hormones are particularly active in the limbic system, which is the emotional center of the brain. That explains in part why adolescents not only are emotionally volatile but may even seek out emotionally charged experiences—everything from a book that makes her sob to a roller coaster that makes him scream. This double whammy—a jacked-up, stimulus-seeking brain not yet fully capable of making mature decisions—hits teens pretty hard, and the consequences to them, and their families, can sometimes be catastrophic.

While scientists have long known how hormones work, only in the past five years have they been able to figure out why they work the way they do. Because sex hormones are present at birth, they essentially hibernate for more than a decade. What, then, triggers them to begin puberty? A few years ago, researchers discovered that puberty is initiated by what appears to be a game of hormonal dominoes, which begins with a gene producing a single protein, named kisspeptin, in the hypothalamus, the part of the brain that regulates metabolism. When that protein connects with, or “kisses,” receptors on another gene, it eventually triggers the pituitary gland to release its storage of hormones. Those surges of testosterone, estrogen, and progesterone in turn activate the testes and ovaries.

After sex hormones were discovered, for the rest of the twentieth century they became the dominant theory of, and favorite explanation for, adolescent behavior. The problem with this theory is that teenagers don’t have higher hormone levels than young adults—they just react differently to hormones. For instance, adolescence is a time of increased response to stress, which may in part be why anxiety disorders, including panic disorder, typically arise during puberty. Teens simply don’t have the same tolerance for stress that we see in adults. Teens are much more likely to exhibit stress-induced illnesses and physical problems, such as colds, headaches, and upset stomachs. There is also an epidemic of symptoms ranging from nail biting to eating disorders that are commonplace in today’s teens. We have a tsunami of input coming at teens from home, school, peers, and, last but not least, the media and Internet that is unprecedented in the history of mankind. Why are adults less susceptible to the effect of all this stimulation? In 2007, researchers at the State University of New York (SUNY) Downstate Medical Center reported that the hormone tetrahydropregnanolone (THP), usually released in response to stress to modulate anxiety, has a reverse effect in adolescents, raising anxiety instead of tamping it down. In an adult, this stress hormone acts like a tranquilizer in the brain and produces a calming effect about a half hour after the anxiety-producing event. In adolescent mice, THP is ineffective in inhibiting anxiety. So anxiety begets anxiety even more so in teens. There is real biology behind that.

In order to truly understand why teenagers are moody, impulsive, and bored; why they act out, talk back, and don’t pay attention; why drugs and alcohol are so dangerous for them; and why they make poor decisions about drinking, driving, sex—you name it—we have to look at their brain circuits for answers. The elevated secretion of sex hormones is the biological marker of puberty, the physiological transformation of a child into a sexually mature human being, though not yet a true “adult.”

While hormones can explain some of what is going on, there is much more at play in the teenage brain, where new connections between brain areas are being built and many chemicals, especially neurotransmitters, the brain’s “messengers,” are in flux. This is why adolescence is a time of true wonder. Because of the flexibility and growth of the brain, adolescents have a window of opportunity with an increased capacity for remarkable accomplishments. But flexibility, growth, and exuberance are a double-edged sword because an “open” and excitable brain also can be adversely affected by stress, drugs, chemical substances, and any number of changes in the environment. And because of an adolescent’s often overactive brain, those influences can result in problems dramatically more serious than they are for adults.