Tell me what we know about what's inside the teenage brain that we didn't know 10 or 15 years ago.

The biggest jump in our knowledge over the last few years is that well into the adolescent period, through 15 or 18 years of age, there are changes going on in the front of the brain that we didn't know very much about even 10 or 15 years ago.

Did we think that the brain had largely been formed early on and that there weren't big changes happening?

We know from some work done about 15 or 20 years ago that there were some changes that clearly continued into adolescence. However, I think many people had mistakenly believed that most of the changes occurred in the first few years of life, and then after a child was about three, there was actually relatively little change occurring.

We know now that's absolutely incorrect. Anyone who's seen a teenager knows that there's a lot of change going on in those years. And it would be foolhardy to think that the brain finished developing at three, but something else was going on at 15.

So what do we know now that we didn't know before in terms of the brain?

One thing that we know now is that there are changes in how information in the front of the brain is transmitted to different parts of the brain and how that information is processed. And we know that these changes seem to increase dramatically after a child enters puberty, and continues probably to the end of adolescence, for the most part.

Anyone who has seen a teenager traverse the area from, say, 12 to 18 knows there's enormous changes and enormous growth in that period of time. We think these changes are brought about by some of the changes going on in the frontal cortex.

What does that area of the brain rule? What does it do?

We've known for a long time that what we actually call the prefrontal cortex, the part that sits behind your forehead, is involved in planning behavior, your use of strategies -- a technical term we call cognitive flexibility, which is: Can you change your mind and do you have sort of a fluid way of going about solving problems? It has something to do with another construct we call working memory. So if I give you a phone number and ask you to remember seven digits, can you remember that for a few minutes until you dial the number? That's working memory. These higher cognitive functions are all performed by the front of your brain.

The other part the front does is that it allows us to regulate our emotion. The seat of our emotion is actually deep in the middle of our brain, but our ability to regulate it is something that emerges as children develop. We've all seen the temper tantrums of a 2-year-old, for example, and we've seen the emotional lability of a 14-year-old. As they traverse into adolescence, the areas of the frontal cortex gradually begin to regulate those emotions that have their seat in the middle of the brain.

What do you mean by "emotional lability?"

An example for a teenager would be their outbursts. They might be perfectly happy one moment and then just turn around and be absolutely miserable and scream, "I hate you, you're the worst parent," and then a moment later, say, "Oh, dear Mom, that was great. Thanks for doing that." And there are cycles which can occur sometimes from a parent's perspective on the order of a nanosecond, although they probably sometimes take minutes. That lability is probably because the frontal cortex is not adequately overseeing the middle part of the brain that actually gives rise to the emotion.

Are there things that we blamed before on hormone surges or attitude -- "this is simply a stage" -- that actually could be explained by a developing brain?

Right. We think hormones play a role in some of this emotional lability, but unfortunately, we don't know exactly what that role is. We say that because we know that during the initial burst of hormones that occurs as a child enters puberty, [is] when the lability can be the most dramatic. As children get to be a year or two post-puberty, that's when things start to level out. But we think the lability itself is probably due to this emotion regulation function done by the frontal cortex. ...

So when young teenagers feel that they are misunderstood, they really have a cause to feel that? In fact, their brain is still developing.

Teenagers -- particularly when they're first becoming teenagers -- have every reason to believe and to feel that no one understands them. They themselves are sometimes surprised at what flies out of their mouth. A personal example is when my son was 12, he one day just blurted something out and then grinned and he thought out loud, "Where did that come from?"

The reason for these things is that they're feeling things before they can regulate and even articulate what it is they're feeling. So they often [let things] fly out of their mouth. And sadly, there's an analogy that sometimes adult patients with damage to the frontal lobe behave just like this as well.

So what does this mean for our understanding of child development as a whole? How does this impact on the work that's been done on early [childhood]?

The recent work on brain development, in my mind, enormously helps explain things that we've known for some time in child development. People who've studied adolescence for many years have pointed to these changes in behavior that we've been describing -- these changes in mood and fluctuations in mood and the like -- without quite being able to pinpoint what was responsible for those changes. Now, I think we have a much better handle on that. My argument would be that it's the changes going on in the frontal cortex that gradually give the child the ability to regulate those powerful emotions, to do things like solve problems more effectively, to be more planful in their behavior.

For example, it's not uncommon for children in, say, seventh and eighth grade to not be very good at doing their homework, because they'll often forget that they have a project due the next day. As they get older, they're better at doing that. These are all skills that are done by the frontal cortex that is unfolding from the time a child starts to enter puberty until probably 15 to 18 years of age. So what's really new here is our ability to explain the child development work that we've known about for quite some time.

If we see that there's an explosion of growth and a great deal of change in this adolescent brain between, let's say, 11 and 15, does this reinforce some people who have said [that] the brain is actually a lot more plastic than people thought, and we should look at the early childhood years?

I think that neuroscientists have felt for many years that the brain is remarkably pliable and remains pliable for a fair number of years. The concept that the first three years of life is when there's the most malleability and, after that, we lose it, is based on a misreading of some of the basic neuroscience work.

For example, we know that there are sensitive periods in how we develop our eyesight, how we perceive speech and language -- that we need to be exposed to things in our visual world and in our auditory world in those first few years for those systems to become set normally. But in terms of our cognitive systems, our intellectual abilities, our emotional abilities -- those have a much longer developmental trajectory. We think that, in fact, the ability to modify one's intellectual potential and one's emotional control and emotional feelings and the like probably remains pliable well beyond the teenage years. ...

Of course, a classic example of that is how effective psychotherapy can be for the treatment of some mental disorders. So there we have a situation where we're actually modifying neural systems that are involved in emotion and we can do that at the age of 20 or 30 or 40 or 50. So there's a case where we can actually point to an example of the malleability of the brain -- the fact that we can acquire second and third languages, the fact that we learn new material throughout our life span -- all examples of this plasticity that you refer to, or this pliability of the brain.

So in fact it was a little bit misleading to think that the door closed at the age of three and then after that, the brain was not very plastic or pliable anymore. The reality is that that's true in only a small number of areas. But beyond the age of three, there's dramatic change.

Why is this debate particularly important?

I think part of the misunderstanding was that, in fact, in the first few years of life, the brain grows more dramatically in size than it does at any other point in time. People interpreted that to mean that because that is the most rapid period of development, it is a critical period of development.

But in fact, after the age of three, although the size of the brain isn't changing all that dramatically, when you look carefully at it, it's the intricate architecture of the brain that continues to unfold for the next decade or more. So this was never a point of contention among those who view the world through the lens of a neuroscientist. They knew that the brain continued to develop for the first one or two decades of life.

The concern was that there was some evidence on the child development side that, unless children had certain experiences in those first few years, that would lead to a bad outcome and this was based primarily on work of deprivation. A good example were some studies that were done on children reared in Romanian orphanages that indicated that if they spent more than sometimes a year or two in those orphanages, their development would be derailed.

The problem is the study of deprivation doesn't tell us much about normal development. And so I think the point of departure came initially when people were pointing to the effects of early deprivation without really understanding that that is not a model at all for how normal development works. ...

What about the classical music being played to children, the flashcards, the mobiles? What do you have to say about that?

I think that I have always been skeptical of this movement to accelerate development among children. In fact, perhaps the most famous child psychologist -- a fellow named Jean Piaget who was very, very prominent in the field of child development for many, many years -- when he first came to the United States and talked about different stages of development that children go through, typically someone from the audience would say, "Well, that's all well and good, Dr. Piaget, but how can we speed this up and get our kids to do this even sooner?" And he referred to that as "the American question."

And in fact, our society has been obsessed with how to give even more advantages to our children, on the assumption that that enrichment will accelerate their development. The fact is there's no evidence for that at all, an example being the classical music exposure, the exposure to Mozart. That was work done entirely with adults. It was never done with babies. And the effects lasted ten minutes and the effects were not only short-lived, but very, very confined.

To go from that, as was the case with Georgia Governor Miller, who systematically gave all infants coming home from the hospital after being born a classical CD, thinking that somehow exposure to classical music would stimulate their brain, had no basis in fact whatsoever.

So if we take the flashcards, if we take the videos, if we take the classical music and we take the French and German lessons for the one-year-old, all of these things are unlikely to yield long-term effects. I think the biggest advantage is that babies are being paid attention to by their moms or their dads or their caregivers in general. It's not that they're necessarily hearing five different languages or that they're hearing classical music or that they're having Shakespeare read to them. There's no evidence that exposure to those things confers any advantage on a child whatsoever.

There is a movement called "I Am Your Child," and there's other groups that work with this movement that have raised what one could say billions of dollars for early childhood education programs. What do you think of that?

There are a number of advocacy groups. "I Am Your Child" is one such group that, on the one hand, I think, has misled the public to some degree by implying that the first three years of life are a critical period in general.

On the other hand, the big benefit they've done to all of us is to point attention to the importance of child development. And I think they get a lot of credit for drawing attention to the importance of thinking that what happens in those first few years is in fact important and that we should not neglect our children. ...

All the evidence suggests that all the things that we should be doing in the first three years of life have the longest benefits if we continue those things throughout the course of a child's life. Anyone who has a teenager knows that a teenager desperately needs contact with his or her parents. They need to be involved in their family. We would be doing an injustice to our children if we thought, "Well, their brain is fully formed, so now we should let them develop on their own."

All parents of teenagers know and all teachers of teenagers know how crucial it is to guide them, influence them and mold them. As much as they resist being molded and influenced, the fact is they still need it. They need it because their brain is still developing, and they need these experiences. A key experience that they get from adults, for example, is how to become more planful, how to have foresight, how to look ahead and realize, "What I'm doing now may have an effect on what happens to me five years from now."

That is extremely difficult for a 13-year-old. But by the time a child is 15 or 16, it's as though a light has gone off and they think, "Oh, my God, I just realized if I bomb this test, if I do poorly in school, if I do this or if I do that, that could have complications or implications for what happens later on."

That's not possible early in life. And that's an example where we need to be with our children all through childhood -- not just the first three years.