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Want to understand your adolescent? Get to know their brain

ERIC DEGGANS, HOST:

What word would you use to describe parenting teens? We're hearing from a brain scientist who says teens are a marvel.

BEATRIZ LUNA: I want people to understand that adolescence is not a disease, that adolescence is an amazing time of development.

DEGGANS: As part of our series Living Better, NPR's Jon Hamilton looks at some new science involving the adolescent brain.

JON HAMILTON, BYLINE: You can find a lot of teenage brains at a skate park like this one in Washington, D.C.

LEO DE LEON: Yo, yo, put me on. Put me on. All right. All right. All right. All right. My name is Leo De Leon.

HAMILTON: How old are you, Leo?

LEO: I'm 13.

HAMILTON: Leo has been skateboarding since he was 10. He says getting the nerve to try a skate park for the first time was hard.

LEO: Yeah, it was kind of scary, but, like...

HAMILTON: How come?

LEO: I don't know. I was, like, scared of falling, but, like, I fell a lot when I first started, and I got hurt a lot.

HAMILTON: Leo also got better fast, and when he'd mastered one trick, he'd push himself to learn a new one, despite the risks.

LEO: I was trying to ollie up something, and then I clipped it. And then my board, like, went up. And then it hit me in my mouth and, like, my braces. So now I have this scar too.

HAMILTON: Leo's also broken his arm, but the payoff is he can do things now, like jump the flight of stairs at the other side of the park.

LEO: I kickflipped that one.

HAMILTON: Yeah? And you landed it?

LEO: Of course I landed it. It's on my Instagram.

HAMILTON: Scientists say all that risk-taking and learning - those are hallmarks of an adolescent brain. Beatriz Luna is a professor of psychiatry at the University of Pittsburgh.

LUNA: It's an incredible brain. It's just perfect for what it needs to do. And what it needs to do is gain experiences.

HAMILTON: A child's brain goes through two critical periods. The first happens about age 2. Luna says the second begins around puberty.

LUNA: Adolescence is the time when the brain says, all right, you've had a lot of time now. We have to start making some decisions.

HAMILTON: Decisions like which connections to get rid of.

LUNA: So you're born with an excess of synaptic connections, and based on experience, you keep what you use, and you lose what you don't use.

HAMILTON: That may be one reason an adolescent brain seeks out new experiences, even if it means a broken arm or a broken heart. Luna says during this period, the brain is also optimizing the wiring it decides to keep.

LUNA: The connections that remain become myelinated. That means they're insulated with fatty tissue, which not only speeds neuronal transmission, but it protects from any further changes.

HAMILTON: Adolescent brain changes tend to start earlier in girls than in boys. And around this time, girls and boys also begin to react differently to certain experiences like stress. Luna says you can see that in studies of teens asked to solve an impossible math problem or give a talk to a group of strangers.

LUNA: Males' blood pressure was higher than females'. However, when people were asked, what did you think about this test, men were like, oh, it was fine, and women were like, I really disliked this. This was extremely stressful.

HAMILTON: Luna says that suggests some differences in certain brain circuits. But sex differences are just a small part of the big changes sweeping through the brain. And Luna says those changes continue throughout the teens and beyond.

LUNA: A lot of times people will think, oh, too late. They're adolescents. But no, because even though it is a time of vulnerabilities, it's also a window of opportunity.

HAMILTON: Leo the skateboarder agrees.

LEO: When you're younger, you're, like - your mind is more open, and you're more creative, and, like, nothing really matters. So you're - you'll really try anything.

HAMILTON: Adolescence isn't just for humans. Alexandra Rosati of the University of Michigan says you can see it in chimps.

ALEXANDRA ROSATI: There's something really charming about the chimps when they're going through this adolescent period. They look kind of gangly. They have these new big teeth in their mouth.

HAMILTON: And, of course, there's puberty.

ROSATI: They're going through this physical change in the body, and those same hormones are re-sculpting the brain basically during this period.

HAMILTON: Part of this re-sculpting involves taking risks. Rosati showed this with a gambling experiment. Chimps of various ages were given a choice. They could go for a sure thing, peanuts, or they could choose a mystery option that was either a meh cucumber or a delicious banana.

ROSATI: Adolescent chimpanzees were more willing to make that gamble, so they were more likely to choose that risky option and hopefully get the banana, whereas adults were more likely to play it safe.

HAMILTON: Rosati says that suggests young humans are predisposed to risky behavior.

ROSATI: The fact that we see these shifts and risk-taking in the chimps suggests that this is tracking something biological. It's not something to do with human culture or the way children are exposed to the media or something.

HAMILTON: Rosati says it's something the brains of both species have evolved to do.

ROSATI: There's a purpose to this kind of risk-taking. There's an adaptive or evolutionary function to it. So for chimpanzees, just like for humans, this period of adolescent risk-taking lets children grow into adults who are learning to live independently.

HAMILTON: So how does the brain of a chimp or a human encourage risk-taking? With dopamine, a naturally occurring chemical involved in memory, pleasure and motivation. Adriana Galvan, a professor of psychology at UCLA, says adolescent brains give larger dopamine rewards than adult brains. That means a bigger payoff from any positive experience.

ADRIANA GALVAN: And so it's a feedback loop because then you start thinking, well, that was pretty good. I'm going to seek out and motivate and do behaviors that get that to happen again. And so that may be a piece of chocolate. It may be hanging out with friends. It may be doing things that adults find risky.

HAMILTON: Galvan says this amped-up reward system also means young brains learn faster from trial and error.

GALVAN: Whether that's by taking some social risks or whether it's by jumping off a skateboard, you know, at a skateboard park, all of that is pushing the boundaries because that is how we learn best. What happens when I do this?

HAMILTON: But Galvan says big rewards and fast learning make the adolescent brain vulnerable to some behaviors that are damaging rather than useful.

GALVAN: And so if the behavior is doing drugs, the brain is saying, oh, OK, this is what I should be paying attention to and devoting my neurons and my pathways to. And so you strengthen that, and eventually that's how addiction happens.

HAMILTON: Which is one reason so many adult smokers picked up the habit as teens. Galvan says that over the course of adolescence, the brain's priorities change. Early on, it gives more attention to positive experiences than painful ones. But then the balance begins to shift. Take Leo, the skateboarder. He says he's more cautious than he used to be.

LEO: I used to do a lot of stair sets - too much actually, because I feel like I'm old now 'cause I can't really do them anymore because they hurt.

HAMILTON: Which suggests that Leo's brain is developing exactly the way it's supposed to.

Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.

Jon Hamilton is a correspondent for NPR's Science Desk. Currently he focuses on neuroscience and health risks.