For Patients and Families

Frances E. Jensen, MD

Frances E. Jensen, MD, senior assistant in Neurology at Children's Hospital Boston and a professor at Harvard Medical School, is translating the most up-to-date research on the teen brain which she shares with parents, teachers and teens during her presentation, "Teen Brain 101".

The teenage brain has previously been thought to be just a young adult brain. But research has shown that is quite different biologically from the adult brain, just as it is different from the children and the baby brain. It's got a different level of ability to learn, but there may also be some vulnerabilities that are still hidden in the teenage brain and this has been a recent focus of research.

Yes, there many misconceptions, I think. First of all, the teenage brain has not been a source of basic science research. There have been a lot of clinical trials and neuro-psychological evaluations of the teen brain and teens' social behavior and education-related behavior but, it's been poorly understood whether the teenage brain is actually substantively different from the adult brain. In fact, we can think of research that we know has been done on, say, the baby brain that has translated into new methods of treating babies with brain injury or early-childhood learning. Likewise, regarding the late-adult brain, the senescent brain, we know that a lot of the work that's been done in basic research on dementia has actually been translated and put to use for new cures and treatments for dementia and how to manage people at the other end of life.

But what's been ignored has been this sort of intermediate zone of the teenage brain, which is not yet fully an adult brain. So what we've tried to do when we've been giving these talks to high schoolers themselves is try to give them a sense of this surge of new information that's available but hasn't been translated yet. Not enough of the basic research about the developing teenage brain has been necessarily put into use with respect to high school education, how they're treated in the legal system, how they might be specifically vulnerable to substance abuse and addiction. We need to get this information across because it is very exciting and will help us understand these kids better and help them create tools for themselves.

The teenage brain is a late-childhood brain. It's not yet a fully mature adult brain. They're at the end of a childhood pattern of brain physiology and have emerging adult patterns. So they're at the crossroads of these two points in development. And as you know, children can learn very quickly, they go through what we cal a "critical period" (synaptic plasticity): Early in childhood, children can learn two or three languages flawlessly, whereas adults struggle to learn a second language with even getting a mild accent under control. So teenagers are still at that peak learning; they're coming down to adult levels but they are still more able to pick things up, memorize and imprint on things than perhaps later in life. Now, the thing is though they also haven't acquired a really important feature of the adult brain, which is how the different brain areas really connect to each other. As we get older, we develop better, stronger connections between our different regions of the brain. And it actually develops from the back of your brain to the front. And, big surprise, the last place to develop and connect is the frontal lobe. This process is called myelination, which is actually a wrapping of the connections to make them conduct signal faster. It's probably how adults compensate for not having the brilliant learning that children have. So the last place to connect is the frontal lobe. Now we know that the frontal lobe has some very special properties. It's what controls insight, judgment, blocks you from too much risk taking behavior - and these are all issues with the teenage brain and teenagers are notorious for risk taking, poor judgment, not really thinking through things properly, yet they can be very sharp at the same time and can be memorizing all these things for the SATs and be whizzing through material. Yet they're not showing judgment. So that's the paradox: they are very, very sharp on the one hand with respect to their ability to learn and their physiology that underlies learning but the connectivity is lagging.

Girls' brains throughout development seem to be reaching maturity 1 - 2+ years before the boys' brains. And we know this process of myelination, of connectivity - the girls appear to myelinate, to cause the closure of this adult process, two or three years earlier than boys. And when you look at brain growth, what happens across development is that your brain grows and then it actually begins to prune itself a little bit as you become adult-like. So the number of brain cells actually comes down a little bit to become adult-like, and you want that, it's a part of pruning that's important. So when we look at when that happens, it happens a little bit earlier in girls than boys. Boys are completing the process into their late teens and early twenties, whereas girls are completing this process of connectivity and the pruning part of the brain more towards the end of the teenage years, middle to end of the teenage years.

Now, given that lag, some people have suggested we consider gender-based learning. It is possible that the girls are ready to learn certain things earlier than boys because they mature sooner. And so one asks whether some subjects could be taught to girls earlier than boys and we might need to consider this in terms of high school curriculum. However, ideally this is not just gender-based. Every individual is going on their own little curve and obviously everybody's different, even two boys are different from each other in respect to when they are actually reaching the end of their brain growth. In an ideal world, teaching to an individual's development would be the best possible strategy.

The interesting thing is that the teenage brain, because it's still hyper-excitable compared to later in life because it still has some child-like qualities, brings with it some vulnerabilities to injury. On, of course, is substance abuse. Substance abuse and addiction actually turn out to use somewhat the same systems as normal learning does. So when you're learning something, you're memorizing and memorizing, and we understand the biology of how brain connections actually strengthen with learning. Now teenagers, probably, as do children, do this learning very robustly. Unfortunately, addiction is kind of a form of learning, as you can imagine the more you are exposed to something, the more of an affinity you have for it.

Recent studies, only in the last five years, have shown that addiction actually does use some of the same molecular biology and physiology as learning. Therefore, teen brains can get addicted faster and stronger than adult brains and teenagers can have a lifelong problem with trying to shed an addiction that has been acquired as a teenager. An addiction any time in life is not good, but this suggests that they are actually more vulnerable. In addition to the addiction issue, the drugs themselves can have more long- term affects on teenagers than even adults. Since alcohol would be a good example, alcohol toxicity can actually cause more brain damage in a teenager than it can in an adult. It's not good at any age but the teenage brain can actually suffer more damage for an episode of severe alcohol intoxication than an adult brain. Another substance that's used is of course marijuana, and the cannabinoids, the chemical term for that, have been shown to affect teenage brains actually to a greater extent than adult brains. This is in animal studies and there are some clinical trials that might be looking at this as well and what has been found is that there is actually more long-term impairment of memory, even up to a week, following one exposure to marijuana. So the effects are actually more long lasting.

There's another study in which nicotine was exposed to adult rats versus teen rats, and they looked at brain activity with an exposure to nicotine. The adult brain activated on exposure to nicotine but the teenage brain was like 10 times brighter with this marker of activation than the adult brain. So it was really, really responding to this addicting substance. When we talk to these kids in the high schools, we are trying to give them this information so they can make their own judgments and learn that maybe they think it's okay to subject themselves to these risks, but paradoxically, the risk-taking behavior, the judgment, the insight is the one thing that this group is relatively weak at. So we're hoping since it is a fact based generation that by giving them facts they actually might hear the facts even though they might not necessarily be able to make that judgment call subjectively on their own.

That's a very good question: Should teenagers be held accountable for their actions? I think we as a society have to think about what environments are we placing teenagers in and what are we holding them accountable to and how unreasonable or reasonable we are being. We do know that they take risks more, you can quantify it on psychological tests and animal studies will show that too. They're going to be taking more risks and they're not quite there with respect to their judgment. There was a Supreme Court debate about this several years ago and was written up in Science as to whether adolescence was akin to mental disability because they were just not there yet in terms of their ability to judge. I think you could obviously see this information stretching into the wrong direction; it's not an excuse for bad behavior. I think that by talking to the teenagers, we are giving them the information and they might make better choices and know when to objectively say to themselves, "oh maybe I'm not equipped to handle this situation yet."

The whole point of the lectures we give is to address teens themselves, not the parents exclusively, not to their teachers. This is the first generation of adolescents that have had access to this kind of information because it didn't exist before. A lot of this stuff we're quoting is from 2006, 2007, so a lot of it's very new. It will take some years before it ends up in text books and health and growth courses, which is where we hope this information will land. So the idea is if we give them a sense that they actually might be more vulnerable to certain things then they might want to make different choices when it comes to substance use or putting themselves at risk. And also to tell them that they have probably better learning capacity now than ever again for certain types of learning and to embrace that and to really try to use this time in their lives.

We have been very pleased with how they have responded. They ask a lot of great questions, they've been very interactive - because they are very interested in themselves, it's a time when you should be interested in yourself, you're trying to figure yourself out. So we've had lots of questions, you know like, "How much sleep do I need?" "What is sleep deprivation doing to my brain?" "Can I get away with this?" and they really want answers. It's a fact-based generation, this is like the information age, they are brokering information all day long and this is a big issue for them. So you give them this information about themselves and some of it is enlightening to them. I mean we had a lot of, "Oh, so that's why I do that." So there's been a lot of that kind of response. I've had other responses from girls saying, "Should we be in different classrooms than boys?" and boys asking, "Why are boys more aggressive than girls?" "Why can't we sit and read these books as easily as our girl classmates?" We have had some sensitive questions about drug abuse and it's a safe place to ask these questions because it doesn't have to be so personal, it can be hypothetical, and we have the facts for them.

Many say, "Oh, this is amazing. You've explained why my kid is this way and now I'm going to be a little bit more patient with that kid. I realize that this kid is not this hateful person who's constantly trying to reject me or being forgetful." It's not necessarily their 'fault' that they are this way and to sort of embrace their energy but to understand that some of these things that they do aren't really their fault. We tend to as parents, because they appear adult-like in size, think that they should be responsible for themselves, and be showing up to appointments on time etc. And they make mistakes, they are not there yet. So the parents are like, "Oh I can just back off a little bit." And that's been really nice to see.

This is an area, that's been overlooked. There was way more excitement looking at the infant brain and at the senescent and older adult degenerating aspects of later in life. A lot of money has gone into those two extremes because they have been very pressing and big health care burdens. But now that we've sort of gone beyond that, we can begin to recognize that there are multiple stages of life for the brain and each of those stages are actually physiologically different from one another. The teen brain, the adolescent/periadolescent brain is in its own little section of development and has some very unique signatures to it. And I think it's a place where a lot of human psychological research as well as basic research will start to come together. We kind of needed the two ends of life to sort of anchor us so then we could move in and understand that there's a huge difference from early life to late life and from early life to adult; so what's going on for the toddlers, what's going on for the school-aged kids, what's going on for the tween generation, what's going on for mid-teens, and what's going on for the early adults? The early adults brain development does not finish until sometimes 23, 24, 25, so there's a whole story there that's probably yet to be mined.

I think it's going to be an area that will have impact on our education and social policies, health policies. We already know that effects of drugs used for treatment for adults for psychiatric conditions, for instance antidepressants, on the teen brain were unexpected. It wasn't really even on anybody's radar screen that these people who are weighing the same amount as their adult counterparts would have any different need of medication compared to the adult. We could understand that a small child would need a smaller dose, they weigh less etc., but teenagers were sort of lumped in with adults.