Are Teenage Brains Really So Different?

Hey everyone—I’ve been reading lots of books as part of my career pivot, and I’m experimenting with different ways of sharing what I learn.

Below is a summary I’ve created of Frances Jensen’s 2015 book The Teenage Brain: A Neuroscientist’s Survival Guide to Raising Adolescents and Young Adults (Amazon). If you like this post, let me know in the comments or via email. Enjoy!

The Teenage Brain - book cover

“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 . . . none of these things are true.”

– Frances E. Jensen from The Teenage Brain

THE TEENAGE BRAIN is a book packed with studies, reports, and technical explanations of the still-developing teenage brain and the consequences this has for… well, pretty much everything in a teenager’s (and parent’s) life. It will appeal to science-minded parents seeking solid evidence about teenage brain behavior to share with their teens in hopes of positively shaping their choices.

My main criticism of Jensen is that she hardly questions the traditional school- and job-oriented definition of success. Early in the book she shares that “it all turned out okay” for her sons because “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.” Well, good for them, but that doesn’t guarantee much as far as I’m concerned. Are they respectful? Are they self-directed?

Jensen isn’t innovative as far as parenting is concerned—she mostly advocates for badgering and monitoring your kids and controlling them with sticks and carrots. But her research and findings do provide a solid foundation in answering the age-old question, What the hell is going on in my kid’s brain? That’s worth something.

[Teenage] brains are both more powerful and more vulnerable than at virtually any other time in their lives.


The first president of the American Psychological Association, Granville Stanley Hall, set the stage for the modern conception of adolescence in 1904 by describing it as a period of primitive, wild exuberance between the anarchy of childhood and the reason of adulthood. He advocated that adolescents “should be corralled, then indoctrinated with the ideals of public service, discipline, altruism, patriotism, and respect for authority.”

Though he lacked empirical evidence, Hall believed that adolescence was connected to the biology of puberty, which we now associated with “hormones.” He wasn’t incorrect: the main sex hormones (testosterone, estrogen, and progesterone) do surge in adolescence. But, Jensen contests:

“…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? Or course not. We know, simply, that three-year-olds haven’t yet figured out how to control themselves.”

Teenage brains are “seeing” hormones for the first time, says Jensen, so we need to cut them some slack. “…teenagers don’t have higher hormone levels than young adults—they just react differently to hormones.” The“hormones” boogeyman is only small part of the story.


Jensen reviews the basics of brain science, with which you’re probably familiar. (Ever heard of a neuron?) The brain is divided into four lobes; the infamous frontal lobe is what controls executive function, judgement, insight, abstraction, planning, and impulse control. When you hear someone say that “teen brains aren’t fully formed,” it doesn’t mean that they’re missing their frontal lobe, it’s just not wired properly to the rest of the brain:

“…the connectivity of the brain slowly moves from the back of the brain to the front. The very last places to ‘connect’ are the frontal lobes. In fact, the teen brain is only about 80 percent of the way to maturity. That 20 percent gap, where the wiring is thinnest, is crucial and goes a long way toward explaining why teenagers behave in such puzzling ways—their mood swings, irritability, impulsiveness, and explosiveness; their inability to focus, to follow through, and to connect with adults; and their temptations to use drugs and alcohol and to engage in other risky behavior. When we think of ourselves as civilized, intelligent adults, we really have the frontal and prefrontal parts of the cortex to thank.”

The brain is composed of gray matter—neurons—and white matter—the connective links between neurons characterized by the fatty, white, insulator-like substance called myelin. The full “myelination” of the brain doesn’t finish until the early- to mid-twenties.

Myelin is really incredible stuff:

“By essentially ‘greasing’ the ‘wires,’ myelin allows signals to travel down axons faster, increasing the speed of a neural transmission as much as a hundredfold. Myelin also aids the speed of transmission by helping to cut down the synapses’ recovery time between neural firings, thereby allowing a thirtyfold increase in the frequency with which neurons transmit information. . . [the combination is] roughly equivalent to a three-thousand fold increase in computer bandwidth.”

The cortices of babies contain little myelin, which explains their sluggish reaction times. As their motor and sensory areas become more “wired” with myelin, they gain the ability to balance and walk. Around age two, the areas responsible for language and higher-level motor coordination become wired, enabling speech and fine motor skills. This also explains why multiple sclerosis patients can lose the ability to walk and talk: MS destroys myelin.

And here we reach the main point of the book: the disconnect between brain power and brain connectivity. While gray matter density peaks in girls at age eleven and in boys at age fourteen, myelination is still ongoing, so teenagers find themselves in a strange situation. “It’s important to remember that even though their brains are learning at peak efficiency, much else is inefficient, including attention, self-discipline, task completion, and emotions.”

…adolescents have a window of opportunity with an increased capacity for remarkable accomplishments.


Jensen remarks on how teenagers are often fascinated by the neuroscience of their own brains—and how some then use it to excuse extreme or unsafe behavior. Her response: “Your brain is sometimes an explanation; it’s never an excuse.” She continues:

“Your teenagers are knowledgeable and self-aware enough to know that they are not automatons, and this means they have the capacity to modify and the responsibility for modifying their own behavior. . . . brain science isn’t an excuse for crazy, stupid, illegal, or immoral behavior. It’s an explanation and a framework, about which they should be encouraged to read more.”

I love this. It reminds me of the Myers-Briggs Type Indicator (MBTI) personality system, and one its most important caveats: your personality type is not excuse for bad behavior. It’s a way to discover your natural strengths and weaknesses, and then emphasize those strengths and (do your best to) compensate for those weaknesses.

The chief predictor of adolescent behavior, studies show, is not the perception of risk, but the anticipation of the reward despite the risk.


If you’re still insistent that teenagers have to get up early because “that’s what working adults do,” Jensen has some news for you.

Teenagers really do have different sleep patterns from children and adults: they wake up later and go to bed later. They need an average of 9.25 hours of sleep a day, because their brains are processing all the intensive learning that’s taking place. Around nine or ten o’clock at night, teenagers are experiencing a “no sleep” zone, in part because melatonin (the hormone that induces sleep) is released two hours later in their systems than an adult’s. Upon waking, adults have very little melatonin in their systems, whereas teenagers still do, leading to a groggy feeling.

The tragedy is that only about 15 percent of American teenagers get the sleep they need on a regular basis, and most sleep fewer than 6.5 hours a night. The main culprit for this, of course, is school:

“Teenagers can be, and are, forced to abide by the adult chronotype, with early rising for school. However, this early rising does not result in an early bedtime: the teen brain doesn’t adjust at the other end of the day, and instead has a tendency to hold on to that part of its pattern. The result is a shrunken sleep period. However, on weekends, one sees teenagers immediately slip back into late-morning awakenings, as their internal clock prefers. If they are allowed to sleep as long as they like, teenagers will get around 9 to 10 hours of sleep per night. But if they are made to wake up for school . . . they are chronically losing 2.75 hours of sleep daily.”

Good god, 2.75 hours a night of chronic sleep deprivation! We may look back one day and consider this a special form of cruelty that we inflicted upon generations of young people.

Jensen recaps the important of sleep for learning, memory, performance, avoiding depression, improving health, and circumventing the need for stimulants like energy drinks, Ritalin, and Adderall… but is this really news to you? You’ve surely seen how your own life suffers when you’re chronically underslept. I don’t think we need more science to prove this: we need to get serious about pushing back school start times, not stereotyping sleeping-in as “lazy” behavior, and otherwise accommodating our teens’ physiological need for 9+ hours of high-quality sheep-counting each night.

Encourage your teens to turn off their phones at night (or at least disable all notifications) and avoid bright, backlit displays (phones, computers, TVs) for an hour before bed. Jensen cites studies from Japan and New York that show the deleterious effects that electronics have on our sleep—but again, you already knew this. Actually doing it is the hard part. Lead by example and your teen will be more likely to follow.

Infants and children are “larks”; that is, they wake up early and go to sleep early. Adolescents are “owls,” waking late and staying up until the wee hours of the morning.


“…a person’s reasoning abilities are more or less fully developed by the age of fifteen. In fact, adolescents appear to be just as adept as adults in their ability to logically assess whether a certain activity is dangerous or not. This is why teens can, in fact, get very high scores on aptitude tests, such as the SAT, which relies wholly on logic and rational deduction. So why do teens do some of the crazy things they do? In general, teen brains get more of a sense of reward than adult brains . . . the release of, and response to, dopamine is enhanced in the teen brain. This is why sensation-seeking is correlated with puberty, a time when the neural systems that control arousal and reward are particularly sensitive. But because the frontal lobes are still only loosely connected to other parts of the teen brain, adolescents have a harder time exerting cognitive control over potentially dangerous situations.”

Yup, teens prize rewards over risks. They want those sweet hits of dopamine. They want positive feelings now, not later. If you’ve ever met an actual teenage human, this is clear.

But this also means teens are at higher risk for various types of addiction, and they’re less responsive to rehab. So what can we do to help them avoid making some Really Bad Decisions now that may cost them dearly down the line?

Jensen throws a litany of facts and figures at us about the harms of cigarettes, alcohol, and hard drugs on the teenage brain—but her only real intervention suggestion is education. “Whether it’s drug experimentation or car racing, help them visualize the costs versus benefits through an analogy.” Okay, yes, thank you. Parents: talk to your teens about drugs. And if you’re looking for scary research to share with your kids, this book provides an endless supply.

Some of the more interesting findings from these chapters include social risk factors:

“…a survey of 934 American teens . . . found that social isolation for girls and a lack of extracurricular activities for boys increased risk-taking behavior. In other words, socializing with friends or playing team sports appeared to have protective value in keeping teens out of risk-taking trouble.”

The link between smoking and alcohol:

“Those who begin smoking in adolescence are also three times more likely to begin using alcohol . . . not surprisingly, smokers are ten times more likely than nonsmokers to develop alcoholism.”

And the risks of early alcohol consumption:

“…children and adolescents who begin drinking before the age of fifteen are four times more likely to develop alcohol dependence later in life than those who begin drinking at the legal minimum age of twenty-one.”

Jensen’s research comes down pretty hard on marijuana: if you assume that smoking pot is entirely harmless, it’s worth reading this chapter to challenge your preconceived notions.

Adolescents believe they’re adults, and though we know better, the more you treat them that way, the greater the chance they’ll actually try to act that way, too.


This book is impressively long: Jensen goes on to take a crack at teenage stress and anxiety, the Internet and gaming, brain-based gender differences, sport concussions, emerging adulthood (ages 18 to 20-something), and juvenile punishment in the legal system. The latter chapter is by far the most interesting, as Jensen has appeared as an expert in multiple Supreme Court cases involving underage felons, testifying on the underdevelopment of their decision-making systems. Below I share more interesting nuggets from these chapters.

  • Modest amount of computer gaming is associated with positive brain growth, while hardcore gaming (60 hours a week) is associated with brain shrinkage and white matter abnormalities.
  • Adolescent girls develop organizational skills before adolescent boys, leading a to big differences in study habits and testing abilities. Jensen takes aim (appropriately) at the European tradition of tracking young people into college-bound or vocational paths around age 10-11, exactly when the organizational gender disparity is largest.
  • Thanks to their lack of frontal lobe connectivity, teens are more likely to engage in criminal behaviors as part of a group (“half of all homicides committed by juveniles involved multiple accomplices”); they’re less likely to understand their Miranda rights; and they’re more prone to making false confessions than any other age demographic.

It’s as if the brain affects virtually everything a young person does! Oh wait… 🙂

This is really interesting stuff. As long as we don’t use it as an excuse to infantilize teenagers—or justify their sometimes-reckless behavior—I think brain science will continue to offer an excellent foundation for understanding teens’ decisions and empathizing with their actions.

Ultimately, you are your child’s first and most important role model. Your children are watching you, even though they may not even be conscious of it. How you approach your own life, how you confront your own challenges, provides learning experiences for them, so share it with them without overwhelming them. You are a team, after all.

Originally published February 8th, 2018.



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