Teenagers can sometimes feel like a different species. According to neuroscientist Sarah-Jayne Blakemore, who gave this fascinating talk at TEDGlobal 2012, this isn’t a coincidence. While 15 years ago it was assumed that brain development was completed in childhood, scientists now know that the brain continues to develop through a person’s 20s and 30s. The adolescent brain is still a work in progress.

“Teenagers are often parodied, sometimes even demonized, in the media for their typical teenage behavior — they take risks, they’re moody, they’re very self-conscious,” Blakemore says in her talk. Even Shakespeare, she says, made jabs at teens. “But what’s sometimes seen as the problem of adolescence shouldn’t be stigmatized. It actually reflects changes in the brain that provide an excellent opportunity for education and social development.”

So what exactly is different between the teenage and adult brain?

For starters, the limbic system — which gives a person a rewarding feeling after taking a risk — has been found to be hypersensitive in adolescents. At the same time, MRI studies show that teenagers experience a dip in the level of gray matter in the pre-frontal cortex — the part of the brain involved in decision-making, self-awareness, planning for the future and inhibiting inappropriate behavior.

“That might sound bad, but this is a really important developmental process,” says Blakemore, the head of the Developmental Group at the UCL Institute of Cognitive Neuroscience. “The synapses that are being used are strengthened, the synapses that aren’t being used are pruned away. You can think of it a bit like pruning a rose bush … this process fine-tunes brain tissue.”

While adults are generally adept at reading gestures and facial behavior to understand what people are feeling — functioning that occurs in the medial pre-frontal cortex — this area of the brain is still developing in adolescence too. “So if you have a teenage daughter or son and think they have trouble taking other people’s perspectives — you’re right, they do,” says Blakemore.

Listening to Blakemore’s talk definitely makes my own teenage years make a lot more sense. When I was a teenager, I needed a lot of attention, which meant having bright blue hair and wearing the most outlandish things I could find — perhaps a hypersensitive limbic system at work? This got me curious — what were other TEDsters like when they were teenagers? Below, see what people had to say in this TED Conversation about the topic.

“As a teenager I thought adults were dumb and boring; I argued with my parents almost every day. I thought, ‘I’ve got the world all figured out.’ My thoughts of love were shaped by the lyrics of Westlife, The Spice Girls, Boyz II Men, Backstreet Boys and Celine Dion. I read philosophy books, wrote short stories, and loved the piano. I was sure that I would be in the film/media industry; but I had an exaggerated impression of my talent and underestimated the hard work and persistence that would be needed.” —Feyisayo Anjorio

“The world was just opening up to me. I was a nerd and athlete, and thought teachers were the greatest people. I tried to fit in with (what I thought) was the cool group. Overall, high school was great — now I like to take walks and have talks with my kids to find out who they are and where they are at in their thoughts on social issues.” —Antoinette Carvajal

“I’m only just a teenager now, but you can say I’m an obsessive computer/math nerd with rarely any need for social aspects in life.” —Patrick Quinn

“I wore the then-ubiquitous outfit of tie-dye and jeans, very long hair, bare feet, rock ‘n roll and oldies. Youth at that time embraced the comfortable and casual. My hair is shorter now but anyone would recognize me, as my current choices are not so different. There were physical risks I took then of various kinds that I would no longer take once I had children who were dependent on me to be safe and in one piece. I was wary of some but not all adults, specifically those with big and irrational tempers that seemed to consume them. I remain wary of the same sorts of people. I was independent minded both then and now.” —Fritzie Reisner

“I had no idea how brain worked — all I wanted to know was how I could influence others and their decisions to sell my stuff to them. This means I was a salesperson since I was quite young. The older I got, the more things widened up for me. I started to study Behavioural and Influential Psychology to find out more about power and flexibility of human capacity and its vulnerability.”—Edwin Nazarian

What were you like as a teenager? Chime in by adding to this ongoing TED Conversation. I’ll be adding responses to this post throughout the day.

“Fifteen years ago, it was widely assumed that the vast majority of brain development takes place in the first few years of life,” says professor Sarah-Jayne Blakemore, who heads up the Developmental Group at the UCL Institute of Cognitive Neuroscience. “Back then we didn’t have the ability to look inside the living human brain and track development across the lifespan.”

But that’s all changed. Blakemore’s work is now devoted to understanding how and when the human brain develops using technology that lets us do just that. And as it turns out, “It’s not all over in early childhood, but continues right throughout adolescence and into the twenties and thirties,” she says.

First, a definition of what she studies. “Adolescence is defined as the period of life that starts with the biological, hormonal and physical changes of puberty and ends at the age at which an individual attains a stable, independent role in society,” she says. The audience chuckles, and she acknowledges: “It can go on a long time.”

Brain-wise, the most dramatic change during those years happens to the prefrontal cortex, the area of the brain involved in high level cognitive functions such as decision-making, planning, social interaction and self-awareness. MRI studies show that this region undergoes quite dramatic change during adolescence. In fact, there’s a significant decline in the prefrontal cortex in adolescence. “That might sound bad, but it’s really important,” says Blakemore. We should think of it like pruning a rose bush, she advises. Just as you might prune away weak branches to ensure the remaining branches stay strong, the brain is finetuning itself.

Blakemore is particularly interested in the social brain, and she and her team are working to understand the network of brain regions we use to interact with other people. She shows a photograph of footballer Michael Owen, who has just failed to score a goal, in front of a crowd of crushed fans — every single one of them with hands on heads, faces contorted in identical pain. ”The picture shows us how instinctive and automatic social responses are. Within a split second, everyone is doing the same thing with their arms and faces.” (Except the three guys in the back in the wrong section.)

It’s not just a funny picture; it also illustrates how good we are at reading other people. Yet analyzing both adolescents and adults showed up some interesting patterns. The brain area called the medial pre-frontal cortex is more active in adolescents when they make decisions than it is in adults — which suggests that adolescents really do use a different mental approach to make social decisions. She describe a test that shows that the ability to account for someone else’s perspective is still developing even in relatively late-stage adolescence. So, she says: “If you have an adolescent son or daughter and think they find it difficult to take direction, you’re right. They do!”

That, she argues, is why the demonization of adolescents is unfair. Their brains really are different. She recounts the story of a friend who said that the thing he noticed most about his teenage daughters was their level of embarrassment around him. “Before puberty he’d say ‘stop messing around, and I’ll sing you your favorite song.’” The girls would stop what they were doing and start behaving immediately. “After puberty, that became a threat. The very notion of their dad singing in public was enough to make them behave,” she says. The audience laughs knowingly.

Now Blakemore is trying to understand phenomena such as risk-taking, which activates the limbic system, hypersensitive in adolescents, while the prefrontal cortex, which moderates risk-taking, is still developing in adolescence. Science!

Her work is not only to justify the behavior of young people. Blakemore closes with an exhortation that we should think about the education of adolescents during this crucial period of brain growth. “40% of teenagers don’t have access to secondary-school education,” she says. “This is the period of life when the brain is particularly adaptive and malleable. It’s a fantastic opportunity for learning and creativity.”

Photos: James Duncan Davidson

Stevenson is Executive Director of the Equal Justice Initiative, who represented two plaintiffs in a case before the United States Supreme Court. In Miller v. Alabama and Jackson v. Hobbs, two young men were sentenced to life without the possibility of parole, sentences that were mandated by law. Stevenson argued that laws mandating sentences of life without the possibility of parole for adolescents and children are unconstitutional.

Yesterday, the Court ruled those mandatory sentences unconstitutional. According to Stevenson, ”This is an important win for children. The Court took a significant step forward by recognizing the fundamental unfairness of mandatory death-in-prison sentences that don’t allow sentencers to consider the unique status of children and their potential for change.”

Justice Kagan, writing for the majority, said: “Given all that we have said in Roper, Graham, and this decision about children’s diminished culpability, and heightened capacity for change, we think appropriate occasions for sentencing juveniles to this harshest possible penalty will be uncommon.”

This is not news to TEDGlobal speaker Sarah-Jayne Blakemore. A professor at University College London, she researches the adolescent brain, and has found that there are tremendous changes that take place during that stage of growth. Blakemore, who will be speaking at TEDGlobal tomorrow afternoon, was part of a group of neuroscientists who wrote to the Supreme Court two years ago to argue that recent research has shown unequivocally that the brain shows more development during adolescence than was previously assumed, and that the courts should take this development into account in trying juveniles.

According to Blakemore, these results are the result of new technologies, such as MRI, which allow us to look inside the brain. It’s not surprising that there is an instinct to treat adolescents as adults, she says: “Adolescents can look adult, but they don’t have an adult brain. There’s a paradox there, but we should allow for the development of their brain.”

She is quick to point out that current understanding doesn’t tell us when the brain becomes “adult.” In fact, “The whole concept of the brain becoming adult is kind of a red herring.” Nor do they speak to the concept of free will and culpability. But, she notes, ”Given the new neuroscience data, it just doesn’t make any sense to put minors in prison for the rest of their lives, given that their brains will naturally develop.”

Stevenson warns that this is not the end, and that prejudices still remain. “In applying their discretion in juvenile life-without-parole sentences, judges need to be mindful to avoid a disproportionate impact on children of color.”