BJ Casey — Two Competing Models of the Adolescent Brain

LC: Can you tell me about the old dual system model of the adolescent brain and how the model you’ve recently helped to develop, the imbalance model, differs from that?

BJC: Yeah, so usually when people talk about the adolescent brain it’s about sex, drugs, and rock and roll. The dual system model is about two orthogonal or competing brain  systems, and one is more developed than the other so it basically wins out. The imbalance model is based on imaging studies performed by my former graduate student Dr. Adriana Galvan (now tenured prof at UCLA) to look at the effects of rewards on developing brain circuitry rich in dopamine, which is very important for reinforcement learning in particular. And so the way we think the brain is evolving is related to the way regions are talking to one another or the connections among regions. Are you a Star Trek fan at all, or seen the recent movies even?

I’ve seen at least a couple.

The analogy is that different parts of the brain are like Star Trek characters. Spock, for example, is half Vulcan, so Spock would never say anything to the captain unless he was being irrational or he asked Spock for information. So we think about the brain not as these independent blobs in the brain, but in terms of how brain regions talk to one another. It is similar to a dual system model, except that if we reduce everything to two systems it’s going to be difficult for us to, with any real precision, show how the brain is changing in subtle but functionally significant ways throughout the extended period of adolescence. In other words, a 13-year-old  is different from a 16-year-old who is different from a 19-year-old in the choices they make and risks that they take. I look at connections in multiple brain systems, actually circuits, that are involved in desire, fear, rage, learning, and self-control and how changes in structural and functional connections give rise to these different behaviors across these ages. And when I say “I,” I mean hundreds of researchers and mentees.

I think the connection between that imbalance and risk-taking seems, at face value, reasonable clear. I’m wondering if that model also helps to explain some of the trends we see with teenage anxiety and depression or college-age mental health issues.

Yeah, I used to think I could lock up my son until he was 21 to protect him and then everything would be fine, but that’s not the way the brain works. The brain changes across adolescence in many ways and needs to learn; it’s adapting to every environment and experience. I think we, as parents, too often try to protect our children so that they never experience pain or failure. Almost every student that gets into Yale has been number one in their class until they get to Yale. When I first arrived at Yale it was hard for me to understand how an A- was like an F for some students. This is why very early on we all need to experience some failures or times in which we are not the best,  so that we can learn to handle failure and disappointment on our own so that when we are no longer living with our parents or caregivers that we  can more easily cope when life is not a bowl of cherries.

So you think it’s primarily due to that sheltering.

I think it’s partly due to that sheltering, but I think it can also be due to the stress that so many young people are under due the huge emphasis we place on academics. We need to reinforce all aspects of development including social and emotional development not just cognitive or intellectual development. Empathy could go a long way in this world right now, but we think we have to be the most intelligent to succeed. If we are always focusing on how smart we are… we know there are a fair number of smart people who don’t have the most empathy or appreciation for others. I think it’s all about balance.

This isn’t something that everyone experiences. I mean, unfortunately not everyone can afford an education. We have this sort of prolonged adolescence with these longer periods of education. As my colleague Larry Steinberg would say, that’s probably good for us, having an extended period to learn. However, people who grow up in very dangerous environments probably had to become adults very quickly. Are they experiencing anxiety and depression? Perhaps, but it might come at a different time because they’ve been forced to be an adult so soon in life.

So adolescence is this time when, as you mentioned, in human history we would kind of diverge from our parents’ guidance and develop our sense of identity and self. I think there is now probably more connection with and financial dependence upon parents than ever before. 

Yeah, I just saw an op-ed piece in the NYT on the delaying of adulthood, robbing children of their ability to become pro-social, healthy young adults. Not all parents are helicopter parents, and most parents have good intentions when it comes to raising their children. They want their child not to have to struggle like they did, but sometimes that can do detrimental the child’s development where either the don’t feel responsible or accountable for their actions or they feel too responsible and always feel they have to impress their parents.

Another thing is sometimes we focus on academics at the expense of physical education. We know in adults that physical exercise is associated with greater mental health. We have some preliminary results from the ABCD study of over eleven thousand children that suggests that participation in sports, especially social team sports, is associated with resilience against depression, but we don’t always, in school, emphasize physical education or provide opportunities for all children to take part in sports.

On your website, or on the FABLAB website, there’s a question about “When is an adolescent an adult?” And I got to thinking about these age boundaries in society like 16 to drive, 18 to vote, 21 to drink, 30 to run for senate or whatever… I don’t imagine that when these were made, they were basing them off psychological or brain data of the development stages.

There are arbitrary reasons for how our country defines when an adolescent reaches adulthood. It’s a bit like why we have summer vacations from school. It was originally based on the growing season for farming, so children needed to be home to help out on the farm, but fewer and fewer children live on farms or have to work on them.

Based on our work and others, the time point for when an adolescent has adult capacity varies and hinges on the situation. There are some cognitive abilities where teenagers outperform adults, but in emotionally charged situations or when they have to think about long-term consequences, because they haven’t had as many experiences as adults, they might not consider certain outcomes and make a bad choice in the heat of the moment. They don’t make risky choices because they feel immortal and that they are not vulnerable. Given a survey, young people think that they may be more vulnerable to illness than adults do, even though this isn’t true. It’s just that often they don’t think about how their actions in one moment could impact their future, or, even if they know better, they just cannot stop themselves.

So those psychological capacities take up until the early twenties to mature. There’s an emerging literature showing this. If you’re just making a simple cognitive decision, with no emotion, no social or peer influences—probably by fourteen, fifteen, sixteen you’re already at the developmental asymptote, but add emotions and peers and all bets are off.

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