For parents of a teenager, adolescence can be a difficult time. But for a brain scientist, it’s a marvel.
« I want people to understand that adolescence is not a disease, that adolescence is an amazing period of development, » she says Beatrice Lunaprofessor of psychiatry and pediatrics at the University of Pittsburgh.
This development is on display most afternoons at Shaw Skatepark in Washington, D.C. It’s a public place, full of teenagers who hang out, take risks, and learn new skills at a rapid pace.
« When you’re younger, your mind is more open, and you’re more creative, and nothing matters, » says 13-year-old Leo De Leon. « So you’ll really try anything. »
Leo has been skateboarding since he was 10 years old. But working up the courage to try a skate park for the first time was « kind of scary, » he says. « I crashed a lot when I started. And I hurt myself a lot. »
Leo got better too, fast. And when he mastered a trick, he strove to learn a new one, despite his risks.
« I was trying ollie something, and then I cut it out and my board lifted up and hit me in the mouth,” he says, “so now I have this scar.
Leo also broke his arm and his elbows are a mess. But the bonus is that he now he can do things like jump the five flight of stairs across the park.
« I kicked that, « he says. » It’s on my Instagram. »
Looking for new experiences
Leo’s rapid progress from scared rookie to accomplished skater showcases the strengths of a teenage brain.
« It’s an amazing brain, » says Luna. « He’s just perfect for what he has to do. And what he has to do is gain experience. »
A child’s brain goes through two critical periods of very rapid change.
The first happens around the age of 2 when most children are busy walking, talking, climbing and falling. The second critical period begins around puberty.
« Adolescence is a time when the brain says, ‘Okay, you’ve had plenty of time now, we need to start making some decisions,' » says Luna
Decisions like which connections to delete.
« You were born with an excess of synaptic connections, » says Luna. « And based on experience, you keep what you use and lose what you don’t use. »
It is a process known as synaptic pruning. And its imminent arrival may be one reason a teenage brain seeks out new experiences, even if it means risking a broken arm or a broken heart.
During this time the brain also optimizes the wiring it decides to maintain.
« The connections that remain become myelinated,Luna says. “That means they’re insulated with fatty tissue, which not only speeds up neuronal transmission, but protects against any further changes.”
Sex differences in brain and behavior
Adolescent brain changes tend to start earlier in girls than in boys. And in this period, males and females also begin to react differently to certain experiences, such as stress.
This was a find of a Analysis of research on adolescents asked to perform tasks like solving an impossible math problem or giving a speech to a group of strangers.
« The males’ blood pressure was higher than the females, » says Luna. But when participants were asked about the experience later, males said, « Oh, that was fine, » while females described it as « extremely stressful. »
Luna says it suggests there are some sex differences in some brain circuitry. But it’s not clear whether these differences are the result of genetics, hormones, or social and cultural influences, she says.
Regardless, gender differences are only a small part of the big changes that go through the brain during adolescence. And those changes continue throughout adolescence and beyond.
« A lot of times people will think, oh, too late, they’re teenagers, » says Luna. « But no, because even though it’s a moment of vulnerability, it’s also a window of opportunity. »
Adolescence, chimpanzee style
Adolescence isn’t just for humans. It is also present in chimpanzees.
« There’s something really fascinating about chimpanzees when they go through this adolescent period, » he says Alexandra Rosatti, associate professor of sociology and anthropology at the University of Michigan. « They look a little lanky. They have these big new teeth in their mouths. »
And, of course, they are going through puberty.
« They’re going through this physical change in the body, and those same hormones are resculpting the brain, basically, during this time, » Rosati says.
Part of this resculpting involves a willingness to take risks.
Rosati was part of a team that made a gambling experiment with 40 chimpanzees of various ages in a sanctuary in the Republic of the Congo.
Chimpanzees had a choice. They might go for one sure thing: peanuts. Or they might select a mystery option which could be a boring cucumber or a delicious banana.
“Adolescent chimpanzees were more willing to make that bet,” Rosati says. « They were more likely to take that risky option and hopefully take the banana, while adults were more likely to play it safe. »
This suggests that young humans and chimpanzees are both predisposed to risky behavior.
“The fact that we see these changes in risk-taking in chimpanzees suggests that something biological is being traced,” Rosati says. « It’s not something to do with human culture or how kids are exposed to the media or anything like that. »
For both species, Rosati says, there’s a purpose to this kind of risk-taking. “This period of adolescent risk-taking allows children to grow into adults who are learning to live independently,” she says.
Risky business and dopamine
So how does the brain of an adolescent chimpanzee or human encourage risk-taking? With dopamine, a naturally occurring chemical involved in memory, motivation and reward.
Teenage brains produce more dopamine and are more sensitive to the chemical than adult brains, he says Adriana Galvanoprofessor of psychology at the University of California, Los Angeles.
That means more gain from positive experiences like eating a piece of chocolate or just hanging out with friends.
« It’s a feedback loop, » he says, « because then you start thinking, well, that was pretty good. I’m going to make that happen again. »
This amplified reward system also helps young brains learn faster by pushing the envelope and constantly asking, « What happens when I do that? » Galván says: « because that’s how we learn best ».
But big rewards and rapid learning can leave the adolescent brain vulnerable to some behaviors that are harmful, rather than helpful.
« If the behavior is drug-taking, the brain says, ‘Oh, OK, this is what I should be paying attention to and dedicating my neurons and pathways,' » Galván says. « So you reinforce it. And ultimately that’s how addiction occurs. »
The brain’s vulnerability during adolescence is probably one reason why so many adult smokers picked up the habit as teenagers, Galván says.
Over the course of adolescence, though, the brain’s priorities change, he says. In the beginning, she pays more attention to positive experiences than to painful ones. But then, the balance starts to shift.
It seems to be happening with Leo the skateboarder.
« I used to do a lot of sets of scales, » he says. « I feel like I’m old now because I really can’t do them anymore because they hurt. »
All of this suggests that Leo’s brain is developing exactly as it should.