Watch the replay of this event held April 26, 2023. (Transcript below.)

It may be difficult for older adults to fathom, but today’s teenagers have never lived in a world where depression, anxiety and other mental health disorders weren’t rife — and on the rise — among their peers. Just a few decades ago, many psychiatrists thought depression was a condition that affected only adults. Now we know better: Researchers think more than half of mental health disorders, including depression, begin by age 14.

The teenage years are a dynamic period of brain development, when neuronal connections undergo intense remodeling and pruning. This flexibility allows teenagers to learn quickly and adapt to a changing environment, but it can also make them vulnerable. Many questions have yet to be answered, such as why the risk of mental illness increases severalfold during adolescence, why some teens appear more resilient to mental health problems than others, and when the brain should be considered “mature.”

On Wednesday, April 26, join leading neuroscientist BJ Casey and teen mental health advocate Diana Chao for a conversation with Knowable Magazine and Annual Reviews about the teen brain’s unique strengths and challenges, and why many experts have declared a global mental health emergency in children and adolescents. We’ll talk about what adults can do to support the teenagers in their lives — and crucially, how teens can help one another.

This event is the second in a series of events and articles exploring the brain across the lifespan. “Inside the brain: A lifetime of change,” is supported by a grant from the Dana Foundation.

Register here for “The baby brain: Learning in leaps and bounds” and “The mature mind: Aging resiliently.” If you can’t attend the live events, please register to receive an email when the replays are available.


BJ Casey

Neuroscientist, Barnard College-Columbia University

BJ Casey is the Christina L. Williams Professor of Neuroscience in the Department of Neuroscience and Behavior at Barnard College-Columbia University. She pioneered the use of functional magnetic resonance imaging to examine the developing human brain, particularly during adolescence. Her scientific discoveries have been published in top-tier journals, including Science, Nature Medicine, Nature Neuroscience and the Proceedings of the National Academy of Sciences. She has received the Association for Psychological Science Lifetime Achievement Mentor Award and the American Psychological Association Distinguished Scientific Contribution Award. She is an elected member of the American Academy of Arts and Science.

Diana Chao

Mental health activist and founder of Letters to Strangers

Diana Chao founded Letters to Strangers (L2S) when she was a sophomore in high school, after bipolar disorder and a blinding condition nearly ended her life. Today, L2S is the largest global youth-for-youth mental health nonprofit, impacting over 35,000 people annually on six continents and publishing the world’s first youth-for-youth mental health guidebook for free. Chao has been honored by two US presidents at the White House and named a 2021 Princess Diana Legacy Award Winner, a 2020 L’Oréal Paris Women of Worth and a 2019 Oprah Magazine Health Hero. Chao studied geosciences at Princeton University and works as a climate scientist for Kinetic Analysis Corporation.


Emily Underwood

Science Content Producer, Knowable Magazine

Emily Underwood has been covering science for over a decade, including as a neuroscience reporter for Science. She has a master’s degree in science writing from Johns Hopkins University, and her reporting has won national awards, including a 2018 National Academies Keck Futures Initiatives Communication Award for magazine writing.


This event is part of an ongoing series of live events and science journalism from Knowable Magazine and Annual Reviews, a nonprofit publisher dedicated to synthesizing and integrating knowledge for the progress of science and the benefit of society.

The Dana Foundation is a private philanthropic organization dedicated to advancing neuroscience and society.


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Emily Underwood: “Hi, everyone. I am your host, Emily Underwood. On behalf of Knowable Magazine and Annual Reviews, welcome. Today we’re going to be talking about teenagers and what makes adolescence such an exciting and also vulnerable time for brain development.

“First, I’d like to introduce BJ Casey, who is the Christina L. Williams Professor of Neuroscience in the Department of Neuroscience and Behavior at Barnard College, Columbia University.

“Welcome, BJ. Hi.”

BJ Casey: “Thank you.”

Emily Underwood: “OK, please next welcome, Diana Chao, founder and executive director of Letters to Strangers, a youth-to-youth mental health nonprofit.”

Diana Chao: “Hello.”

Emily Underwood: “Hey, Diana.

“Thanks to both of you so much for joining us today. Glad to have you here. OK, let’s dive right in. I’d like to start with you, Diana. You are a Princeton grad now and a climate scientist, and you are also leading this nonprofit, but you have been advocating for young people since you were a sophomore in high school. So I would love to hear a little bit about you and what was going on for you in high school that made you want to help other teenagers.”

Diana Chao: “Yeah, so thank you for asking that question. A little bit of trigger warning ahead for folks. I immigrated to the US from the poorest province of China when I was nine years old. And around that time, as a first-generation immigrant, we, like so many others, met with the 2007, 2008 economic recession, and we quickly lost everything. So I was growing up underneath the poverty line with my parents, who did not speak English at all, and I was trying to assimilate and find my identity in a town that was vastly, vastly majority white. And so over time, especially because I was growing up in a very abusive household, I started to believe in everything that was said about me, that blamed everything upon me.

“And by the time I was about 13 years old, I was diagnosed with bipolar disorder. And then later on that summer, an eye disease ended up making me go blind every time an episode struck. So I was blind for about half of high school. During this whole process, I became severely suicidal and I attempted suicide, at which point my little brother found me. Due to my family situation, I was basically his guardian. And so to have who I viewed as a son of sorts see me in that state made me feel like even though I didn’t care at the time what happened to me, I cared what happened to him. I owed him something, I needed to do something to heal. And I had such a hard time navigating the American healthcare system for many reasons, as you can imagine.

“And so I ended up turning to writing letters, and as I wrote these letters to strangers, I started to find my own voice, I started to develop empathy for people I’d never even met, and I questioned why I couldn’t do the same for myself. So that became the impetus for starting Letters to Strangers as a student club in my high school, my sophomore year. And then over time, I think other people related to me, to the fact that someone who looked like them was talking about these things. And eventually it grew to what it is today, the largest global youth-for-youth mental health nonprofit.

Emily Underwood: “Thanks so much. And you have chapters all over the world, right? So that is something that our attendees who are also from all over the world should look into.”

Diana Chao: “Yes.”

Emily Underwood: “And we’re going to touch on so many of the things you just brought up in our conversation today. So BJ, at about the same time that Diana was launching her nonprofit, you had built a distinguished career as a neuroscientist, studying brain development in children and teenagers using brain scans. So I know you really did some of the first neuroimaging studies of teens starting in the ’90s. What question did you start out wanting to answer?”

BJ Casey: “This is a great question, and I think if I provide a little bit of a historical background, that will help. In the 1990s we had imaging tools like magnetic resonance imaging, or MRI, where we could see beautiful detailed pictures of the developing brain, but we really couldn’t see functional activity without using invasive techniques or ones where we really couldn’t see the fine detail. And so finally, when the functional imaging capacity emerged, we really viewed the brain from a... I’m going to say in a very simple way — we thought of it as growing just like height and weight, so like a growth chart.

“And we expected everything to be linear. And the questions that we primarily had were about regions in the brain such as the prefrontal cortex because of its importance in everyday activities, including planning or multitasking, which we all are doing these days, and also in self-regulation. And what I mean by that is being able to regulate our thoughts, our actions, our desires, and our fears. So that was really what we were trying to understand: What are the mechanisms, what aspects of the brain are changing that help us learn to regulate ourselves?”

Emily Underwood: “So you’re looking at how activity changes in the brain. I’m curious, what have we learned that maybe was surprising about that, that challenged conventional wisdom?”

BJ Casey: “So I don’t know if it was conventional wisdom, but I still hear it today, and I think it’s a common belief — and that is describing the adolescent as really having no brain or prefrontal cortex, the equivalent of being a defective car with only an accelerator. And that was really attributed to the fact that the prefrontal cortex that I described before was still maturing. But by that logic, children should be doing even more risky and somewhat bizarre… should show those behaviors even more than adolescents because they have a less developed prefrontal cortex. And so we began to realize that there’s not this one area of the brain, like a little person that’s driving us in terms of what we say and think, but we need to really consider the development of other brain regions and circuits that are communicating with the prefrontal cortex.

“And one that’s involved in our emotions, desires, fears and stress — the limbic system — is one that shows peak activation during this adolescent period. And so that began to help us understand situations in which adolescents can make decisions as well as adults, and when they have difficulty. And when they have difficulty, is an emotionally charged situation, these changes that are happening in the limbic circuitry is sort of hijacking the prefrontal cortex that’s still developing. And so even when you know better, sometimes you engage in a behavior that leads to bad outcomes. But, very important to know, in non-stressful situations, they’re not emotionally charged, you really see very rational and thoughtful decision making in teenagers. So they do have a brain and they do have a prefrontal cortex.”

Emily Underwood: “I think even when I was in high school, the sort of cliche about teenagers not having big chunks of their brain in place yet was common. So I’m curious, Diana, when you were in high school, what did you learn about the brain? Was it part of your curriculum? What were you hearing as a sophomore?”

Diana Chao: “So I honestly didn’t really learn anything about the brain from school, but I will say that my senior year of high school, I did take IB Psychology. And so in that class we learned a little bit about the brain, we learned about neurotransmitters, things like that. But if you weren’t someone who elected to take that class, you would never have knowledge of those things. And I think the fact that even as that knowledge, like BJ was saying, of understanding that actually teens do have a brain, even as that knowledge was becoming more scientifically backed, many of the teachers were still operating off of the assumptions that had been in place for so long. So it was very much a situation where even as teens felt like that desire for autonomy and that feeling of, ‘I can have autonomy,’ it was very difficult to get that point across and be heard by those teachers.”

Emily Underwood: “I’m curious if there was something you could have asked a researcher like BJ, or BJ herself, at that time when you were really struggling, what would you have asked?”

Diana Chao: “I think there’s two sides of the same coin, which first is a lot of times people would dismiss what I was going through as just typical teenage angst, but I didn’t feel like that could be right when I actively wanted to kill myself all the time. And so I would have wanted to know, ‘Is this normal? What am I supposed to be feeling?’ But then on the other side of that same coin, that, ‘Is this normal? is also a question for myself because there was so much doubt about if maybe I was a monster, if maybe I was someone who was unlovable. So having a mental illness, does that mean there’s a defect? Something like that.”

BJ Casey: “Do you feel like you’ve learned or that neuroscience has provided insight into the lived experience of adolescence for you?”

Diana Chao: “I think a combination of neuroscience and developmental psychology, all these things, have definitely helped elucidate a lot of things for me. One, to help understand that these things do happen and our brain can have illnesses like any other parts of our body, and that has helped a lot. Another thing I think that has just been super helpful with neuroscience is of course all the advancements in treatment options and understanding our neural pathways that have emerged since. It has given me a bit more hope for sure. And I think we’ll be able to hopefully see even better advancements in the future.”

BJ Casey: “Yes, we hope.”

Emily Underwood: “BJ, I think that’s a nice transition to a question for you about the types of long-term studies with not just 20 or a hundred, but I mean thousands and thousands of young people. Can you tell us a little bit about the types of long-term studies you’ve been involved in? Why do we need such big numbers? Are we learning something about what ‘normal’ looks like? What are we getting out of those types of studies?”

BJ Casey: “I think this is a really important question, and I want to answer it in two ways. So the first point that I just want to make is that when you’re studying general principles of the development of the brain, you want to make sure that you have a representative group that you’re assessing. And by having large numbers, we can measure more unique experiences, but those contribute to noise or variants sometimes to get these general principles. And so you need really large numbers in order to be able to find these brain-behavior-mental health associations. But the more important point that I want to make is too often with our studies, including some large ones, the sample is typically or majority white, educated, middle class young people who are developing. And so changes that we may see with them in their lived experience is going to be very different from changes that we’ll see in others with lived experience.

“So it’s important to make sure that we have diversity in our sample. And one of the largest studies in the United States right now is the Adolescent Brain and Cognitive Development, or ABCD, study. And in this study we’re following nearly 12,000 children over 10 years. And our goal was to try to have a sample of youth that represented the diverse demographics of the US in race, ethnicity, education and income. And that’s a laudable goal, and we have a close approximation to it, but it’s still not representative. But with the large numbers, then you can begin to look at how different individuals and groups respond to the very different environments. Some of these are extreme. We have individuals who respond to, in the US, with discrimination, with our structural racism here. And being able to begin to examine that, and the uniqueness and specialness of that on the brain, those influences, is important as opposed to really just isolating ourselves to one group of individuals with a very different lived experience.”

Emily Underwood: “BJ, can I ask you to air out one of the phrases you used? You said brain-behavior association. Can you give us maybe one or two examples of what does that mean? You’ve got brain, you’ve got behavior, you’re trying to link them together. Can you explain what that looks like?”

BJ Casey: “Right. So many times, we’ll see two things happening in time. It doesn’t mean that they’re related, but in these studies, really trying to see to what extent changes in one brain region like the prefrontal cortex — let’s just say since I’ve mentioned it before — how development of that region impacts our ability to hold on to many items in memory and to prevent the interference or competition from other information that’s coming at us. And so we can see those associations, but they’re relatively small because different people have different experiences that can impact prefrontal function.

“And one of the things we know about chronic stress is it can have devastating effects on the functioning of the prefrontal cortex because you see an increase in what Diana was describing in terms of neurotransmitters that she learned about — those neurochemicals can get so high that they can almost take the prefrontal cortex offline during these stressful periods of time, so that you’re basically functioning with these emotional centers that show elevated activity during this time. So really it’s linking behaviors and environmental factors or influences like stress, and how too they change brain and how is that related to how well someone can remember items. And then we also link that to individuals with mental health problems. And we have work, which I could add to the chat at some point, where we’ve looked at even stress like community violence has an impact on prefrontal functioning in children. Is that an example?”

Emily Underwood: “Yeah, no, that helps. I think what I want to try to do is separate out... So there is this dynamic transformation happening in adolescent brain, but that is not the same as pathology or we don’t need to pathologize that. That doesn’t mean that the adolescent brain is broken, right? But it does mean that there are unique strengths and vulnerabilities going on during that time. Am I getting that right?”

BJ Casey: “Yes.”

Emily Underwood: “OK. So how do you add those things together? Let’s talk about the strengths, first of all. And I think I would like to hear from both of you about the strengths of the adolescent and youth brain, because I think that Diana’s letter-writing exercise and the sort of communication she’s doing and encouraging among youth is a really interesting example of some of the strengths that adolescents can have. So maybe, Diana, you want to start with what you see as the strengths of young people?”

Diana Chao: “ I think, especially with how digitized everything is, there is a broader sense of community. And I would say that looks like an intergenerational thing as well. Like definitely, of course, in the past you have people say like, ‘Oh, my parents don’t understand me, my grandparents don’t understand me,’ but we’ve never seen such a rapid digital tech-based divide the way that our generation and younger have faced. And I think that has caused a very real problem in communication among different generations. So having that youth peer support system is critical to feeling like you can be understood by somebody. And I think that is definitely a strength that young people have today.

“And another thing I’m sure BJ will talk about is neuroplasticity, when we can adapt to things more easily and learn from them, but I think the most important thing is almost like... They always say teenagers feel like you’re superhuman. Like, ‘Oh, you can just do whatever and you’ll figure it out.’ And sometimes it leads to really dumb decisions, I completely agree. But I think other times it also means that when something bad happens, we do have the capability oftentimes of trying to come back up and figure out another step forward. And it doesn’t always work out perfectly, but I think that the ability to still see hope in things is something that can really easily get lost over time. So I want to keep that as a strength for many people.”

Emily Underwood: “I love that.”

BJ Casey: “I do too. I really love that. I mean, I have often talked about the teen brain as a beautiful brain, because I think in many ways it’s evolved to help the teen meet all the many demands on them at this time. I mean, they’re huge. When I give a talk to a large audience, often I’ll ask, ‘Raise your hand if you want to go through the early stages of adolescence again.’ And it’s rare that I get a hand that’s raised. But when we think about this, during these teen years, it’s a period when we’re having really rapid, rapid learning. And it’s also a time when we often find our passions that will be a lifelong passion, and we’re trying to identify ourselves separate from our parents or caregiver, and find our identity, and we need to do that in our social world.

“So I actually think the changes in the brain with this rapid learning, this heightened sensitivity to rewards, sort of pulls us out of our environment to explore more, our heightened sensitivity to threats and stresses. Also as we’re going out into that world, we need to make sure that we can thrive without the buffer or protection of an adult or parent. And it’s also just very important in terms of the heightened sensitivity to peers during this time, which can be such a positive influence in terms of learning about the social rules so that we can emerge then into pro-social contributing members of society. So I see this as a wonderful, wonderful adaptive time, and there’s a lot of extensive learning. Unfortunately, the environments for all youth vary dramatically, and stressors, chronic stressors, are there for many which can exacerbate that sort of imbalance I was talking about before, where you basically get more of an emotional brain being activated relative to one that might be more rational or regulated.”

Emily Underwood: “BJ, we’ve been talking at sort of the macro level. Can we zoom down a little bit to the cellular level for a minute? And there are two words that come up a lot: synapses and myelination. I realize this is a big ask, but can you just briefly tell us what’s going on with synapses and with myelination? What is that? Why is it important during adolescence?”

BJ Casey: “So first, we need to recognize that during development, we have more neural connections, which are called synapses. We have more of those in the brain than we ever will have as an adult. And with age and learning and experience, you see those synapses prune just like we would prune a shrub or bush. At the same time that we are pruning irrelevant connections and keeping essential ones, the fibers that connect brain cells or neurons throughout the brain, those with learning and experience are being strengthened. And so there’s a conductive tissue that wraps around them referred to as myelin, and that makes communication between brain cells and different brain regions faster. And the pruning of those synapses helps with communication between brain systems being more efficient. All of this is exceptional and is continuing to change throughout adolescence to enhance learning. Sort of a general…”

Emily Underwood: “Yeah. Diana, do you have any questions about this plasticity? I’m just curious, with regard to your own condition or the things you’ve heard about, are there questions that you hear from young people about the cellular processes here?”

Diana Chao:“I would say, to be honest, that most people aren’t asking or talking to me about cellular stuff. I think we are just …”

Emily Underwood: “I’m shocked. Shocking.”

Diana Chao: “I’m learning a lot and I really appreciate that. But I think one thing that ends up just sort of being the overall feeling, it’s that same question I had asked earlier, which is just, well, does this mean there’s something wrong with me? Maybe my synapses are not pruning correctly. Or something like, what does that mean for my value as a person? And I think that’s one of the derivatives that people get from these more cellular-based talks.”

Emily Underwood: “Yeah.”

BJ Casey: “So I think that’s a really important point. And I just want to add to that. So it is the case when you have this period of time when we have heightened sensitivity to stressors in the world and we have exceptional enhanced learning that there could be experiences that would strengthen certain pathways that would continue behaviors or thoughts that may not be helpful or healthy.

“So if we have trauma and stresses, we might continue to focus on those stressors and ruminate on them as opposed to coping or trying to reframe and recognizing that there’s a broader world out there, which you wonderfully tapped into that broader network of world and used. And given the brain’s plasticity, even if you’re strengthening a pathway early on, because of its plasticity throughout the life course, but especially in the first few decades, you can retrain the brain to help you reframe and with practice. Then that’s going to be the more automatic response you’re going to have, as opposed to for you to even say, ‘Am I lovable?’ It breaks my heart, but teens feel that way. So I think this is really important point that you raised, Diana. Thank you.”

Emily Underwood: “BJ, do researchers know what it is about the pruning process and the winnowing and the strengthening, do they know why that can lead to increased susceptibility to mental illness at this age, which is quite dramatic, right? There’s a statistical increase in adolescence.”

Diana Chao: “The statistic is something like 50 percent of all lifetime cases of mental illness begin by age 14 and 75 percent by age 24.”

Emily Underwood: “Which sounds really scary.”

BJ Casey: “That’s right.”

Emily Underwood: “Do we know why?”

BJ Casey: “I just wanted to add to those statistics, because it’s the case that if you do experience mental illness, yeah, 75 percent of those occurred before adulthood. And so this is a time in which we see a peak in all the mental illnesses on average, if you look across the board. I don’t think we know or can explain fully how what we were talking about in terms of synaptic pruning and myelination relate to each one of these individual disorders. But again, if you have a system that’s sculpting and learning from experiences and the environment, and you have bad experiences like threats and stress and trauma at a period when you’re particularly sensitive to those, then that learning may occur and those pathways may refine very quickly at this time.

“Another example would be with substance use. So the cause of this heightened sensitivity to rewards too and reinforcement, if you experience those reinforcing properties of drugs and alcohol, those reinforcing properties and its use can actually finetune pathways so that you begin to form habits or addictions. But again, because the brain is plastic and these synapses can change throughout a lifetime, it’s not all or none. We are all a constant work in progress. So you can modify those again and rewire the brain with interventions and therapies that help support incompatible behaviors with that and move you into more healthy responses and behaviors.”

Emily Underwood: “This is all suggesting to me that we should really be paying attention to teens and to sort of what adolescents are experiencing and not, as Diana experienced, sort of write things off as adolescent angst. But that’s probably a tough thing for adults, parents to navigate, right? Because you have this increased risk, you also have a lot of just stuff happening. It’s a really volatile time.

“So I’m curious if you have any suggestions, both of you, for what are some questions to ask if a teenager is reporting distress, to help sort of tease out, ‘Is this just normal? Do they need additional therapy? Do they need medication?’ Obviously that’s not something that a parent can do without a clinician’s help, but what are some of the warning signs?”

Diana Chao: “Yeah, I can get started. I think, and I don’t know if this is a little controversial, but I think the first thing that I would like for us to think about is shifting the perspective from, ‘Oh no, what’s wrong with my teenager?’ to ‘Is there something that I am also doing that might be setting an example for the teenager that I’m not being aware of?’ Because so much of the way that teens and young adults experience these things come from, like BJ said, trauma — and intergenerational trauma is a very real thing. When you look at communities that don’t oftentimes trust the healthcare system, who don’t want to go see mental health support or any type of health support, and let’s say you are a parent and you’re like, ‘OK, my kid needs to seek clinical help,’ but their whole life you have been saying, ‘Oh, these doctors just want to take money from us’ — things like that — why would the kid suddenly feel open to seeing these healthcare professionals?

“And at the same time, I’m not putting the blame on anyone here because I want to point out the importance of history here. In the ’60s and ’70s, the US government funded a program to sterilize Puerto Rican women without any alternative methods of birth control. So by 1968, about one-third of Puerto Rican women were sterilized. And then in the ’60s and ’70s, IHS, Indian Health Services, performed forced sterilizations on one out of every four Native American women without informing them or getting their consent. I point this out because this is going to affect generations of trust between healthcare providers and your own body. And so these are things that are going to affect your children later on in life. And it might be attitudes that you yourself are not aware that you have.

“And so I just want us to also think a little bit about where we are coming from, how we’re having those conversations, and also when you’re having those conversations with your kids, not just, ‘Hey, what’s wrong with you?’ But also, ‘Hey, am I talking about my feelings too in a way that shows the kids that it’s OK to feel vulnerable.’ That maybe, if they’re a guy and they feel like they can’t talk about their emotions, the father figure, if there is one, showing that it’s OK to embrace those emotions and that it’s a healthy sort of masculinity, having those examples set into place so that they learn to open up to you because they’ve seen that you have shown it is OK. I think that is honestly one thing that is often missing in these conversations.”

BJ Casey: “I think those are all really important points. I appreciate you raising them. I’m just going to use the large ABCD study as an example here to make some points. And that is, yes, there’s been real mistrust in the medical and the research community. So trying to…

“We recruited over 600 youth and their families in Connecticut and New York, and that required building trust, and that required not expecting trust. And in a big study like this, when you are working with them for 10 years, they become part of your academic family. And so we are constantly trying to provide resources, not only for parents, but also to empower adolescents and teens to know that they have resources that they can go to. And when you have nearly 12,000 youths in a study, unfortunately there are going to be many, several of those who are going to have mental health issues and some who are going to endure self-harm.

“And so we have a whole series of questions that we ask … that give us an indication of how likely that they would act on this. And then we also make sure that the parents and the child are getting all the positive support or resources that they might need. And then we provide them with hotlines, again — those that the teen can directly contact, as well as the parents. And I think that’s very important.

“Healthy development is a human right. And so we as parents and adults and the community should be making safe environments in which we can allow those very opportunities for youth to learn emotional, social and cognitive skills, to help them become a healthy contributing adult. And this is really, really important. There’s a long way to go in making our world that way. We’re usually just responsive and reactive, and there really needs to be a shift in thinking about interventions and ways that we accept differences in our mental health too.”

Emily Underwood: “BJ, the importance of creating an environment that is supportive to healthy brain development, that came up a lot in our last event on the baby brain, that this is something that starts long before adolescence, that it starts very early, maybe even in the womb, in utero. But what I take away from the uniqueness of this period of development in adolescence is that it’s not all set. Yes, infancy is really important. It all adds up. It’s cumulative, and adolescence is a really important time as well. So it’s not either-or.

“Can we talk a little bit more about the types of interventions for teens that have been studied? I’m curious if the adult brain is different from the adolescent brain, does that mean that we need to treat teenagers differently? Do they need different medications, therapies? What do we know at this point?”

BJ Casey: “Yeah, I really appreciate this question because I think a fundamental issue in psychiatric medicine is really the need for empirical evidence for when, during development, an intervention or treatment will be most effective. And I think that from neuroscience, we’re already identifying windows of maximum change in behavior. We’re also identifying windows when some treatment will be less effective.

“So what we need to do is to treat the developing as opposed to the developed brain and move away from clinical trials which look at the effectiveness of a treatment that collapse children and adolescents because their brains are very different. We now know it’s not like this linear change. It’s not simply like height and weight where you see growth. They’re dynamic changes and adolescent-specific ones that can both put youth at risk, but also are very important in terms of helping them learn to explore and learn how to thrive in their social world as they prepare for an adult role where there’s not a caregiver who’s taking on that responsibility. So yeah, that’s very important.”

Emily Underwood: “Are there any specific examples of a treatment that maybe the data isn’t fully there yet, but it’s pointing at a need to approach it differently?”

BJ Casey: “So I’ll give you one example. These are preclinical data. But if we just look at very simple learning, we’ve learned in rodents and in humans that we can very quickly form a fear memory. That is, if you have a noise that’s paired with a little foot shock, you only have to pair those two together just a few times before children, adolescents and adults, when they hear that tone, they’re going to freeze.

“The interesting thing about adolescents, unlike children and adults, is the ability to then forget that memory or to try not to have fear whenever they hear that tone. There’s a real stickiness or vigilance to threat, which once you form an association, it’s a little bit harder to let go during the adolescent period. And so the reason why this is important in terms of treatments is some of our cognitive behavioral therapy treatments that rely on exposure therapy build on the basic principles of extinction.

“So extinction would just be presenting that tone by itself without the foot shock, right? With desensitization in exposure therapy, you identify what’s triggering the anxiety or stress and then you try to help teach coping mechanisms and strategies and then slowly present those triggers to desensitize the youth. And we think there are ways that we can optimize this for adolescents, since that would be different for children and adults, and get a bigger impact. That’s not to say that cognitive behavioral therapy does not work. There are ways to get it to work for more youth.”

Emily Underwood: “Interesting. That sounds like it might be connected to some of the issues of stress and trauma that Diana was bringing up. OK. We actually need to move to audience questions in just a moment. So I’d like to ask two more questions. One is, Diana, you really hear a lot directly from young people through Letters to Strangers. What advice do you have for teens to help each other? What’s so powerful about letter writing? What do you suggest for teens who maybe are worried about a friend or classmate?”

Diana Chao: “Yeah, I think first thing first is I want to acknowledge that there is more conversation about mental health on social media these days. But what I fear is there’s almost a trendification of it, where people are talking about it more, but oftentimes sort of echoing the same misconceptions or even misinformation. And it leads to this feeling of, ‘Oh, I know more about mental health,’ but actually that information is not accurate. And so this leads to a lot of self-diagnosis and self-medication, which I would heavily urge people to not do, because people go through years of medical training to learn about those things for a reason. But I think the other thing is to be more proactive about the education that we ourselves learn from and seek out.

“And another thing is, I would say to watch your words — learn about how your words matter. So for example, this is something all of us can learn: shifting from saying, ‘Commit suicide,’ to, ‘Died by suicide,’ since ‘commit’ has a criminal connotation and comes from the history of criminalizing suicide. I think the key thing — and this is also for everyone as well — a lot of times we feel confused on what to do when someone needs support because we want to solve the problem and we don’t know what to do.

“But your role is not to be the person who slays the fire-breathing dragon. Your role is to be someone who walks alongside that person as they find the road that they themselves want to go on to heal. I think that’s really important, because in those moments, where someone is in so much pain, at least for me, it feels like you’ve lost all control. The one thing you want to hold onto, one thing you hope you have left is your autonomy and your humanity, and for someone to see you as an individual that you still can be and are. So that’s where I think being that partner, instead of the person who goes in and knows all the answers can be so much more impactful, both as a teenager and as a parent, et cetera.”

BJ Casey: “So positively affirming and supporting. But just to build on that, Diana, I am not trained as a therapist, but you can be supportive and positively affirming of youth and also help them finagle where the resources are that they need when we have those resources available. Yeah. Thank you.”

Emily Underwood: “OK. Are we ready to move on to our audience questions? BJ, if there’s anything else you want to add about how adults can support teens or teens can support? I would love to hear.”

BJ Casey: “I just want to add one point.”

Emily Underwood: “Yeah.”

BJ Casey: “Yeah, I want to add one point because I think this is important. Peer influence is huge on adolescents and it can be positive, and we also know that it’s been associated with negative influences too. But I think what parents and adults aren’t hearing enough is the significant impact they have on the mental health of young people and their children.

“So we know from the ABCD study during the pandemic that two buffers are protective factors for anxiety and stress, mood-related disorders, were family regular mealtimes — so having regularity in this time of uncertainty — and also open communication with parents. The parents play a huge role.

“And then one other thing, and I think this builds in a different way on what Diana said in terms of what parents can do: So often we just focus on the negative. And what’s really important is for us to catch young people when they’re being good, and to reinforce that, given that heightened sensitivity to reward at this time too, so that they really cherish that, and that empowers them and is also supportive. So yeah, those are just my two thoughts there. Thanks.”

Emily Underwood: “Thank you so much. OK. We have a number of questions about screen time and social media. So here’s the question: Given the volume of distractions and screen time that teens experience — phones, online gaming, school-issued laptops, online textbooks — how can we nurture focus and concentration? What are the most brain-healthy habits for them to incorporate in their online time? Diana, do you want to start with that question about screen time, maybe pinging off what you were saying about social media?”

Diana Chao: “Yeah. Oh, I think the first thing to acknowledge unfortunately is that I don’t think we’ll ever really get away from screens. And we have to navigate around that rather than say, ‘Let’s get rid of all screens and that’ll solve the problem.’ That’ll only alienate the kid more from other surroundings and their peers. My brother, he was a huge gamer in high school. And I think one thing that he told me, and we worked on this together, is when he was having a lot of problems with distractions from the screen, there were certain games that forced him to concentrate more than other games. Maybe it’s a timed challenge, maybe it’s something that requires a lot of intricacy and planning, but in those times when he felt really fidgety, he knew that he could game and that was something that his brain was willing to do, that he felt.

“And so if he focused that time on those types of games, then he sort of sets his brain and primes, at least in his mind, to be thinking in that sort of way. So if he’s more used to then focusing on a timed challenge, right after that, he moves down to doing some homework and he sets a timer for himself, he’s a lot more likely to actually be able to complete that than if I just forcibly took the screen away from him and said, ‘Hey, no, do your homework now.’ So I think that’s something that we can think about, is how can we use tools and games and such that they already like and then change it slightly so that we can almost gamify the rest of life so that screen becomes an aid rather than a hindrance.”

Emily Underwood: “BJ, what are your thoughts on this in terms of cultivating attention maybe to do things that are not as fun?”

BJ Casey: “So there’s also the flip side of that, given if you enjoy certain games. And so youths, sometimes, they’ll even self-impose this when they know they have a deadline. It’s like they’ll play that favorite video game after they’ve gotten their work done, because that’s an even bigger reinforcer than anything their parents might suggest.

“Look, social media, screen time, that’s not going to go away, just like when we used to worry about individuals who were bookworms and spent all their time reading books. So there are both positives and there can be negative influences. I think one of the hardest parts with screen time and social media is just how in real time people put themselves out there. And in emotional situations, teens tend to be more impulsive and you can’t take that information back. And so it’s much harder for us to regulate that.

“But during the pandemic, having social media available was really, for some people, the only connection they had with the social world. And so it has its pros and cons, but if I were to say what’s really going to help focus our attention, it’s getting enough sleep and getting exercise and taking care of ourselves. And often when we’re spending a lot of time, screen time, we’re not getting the exercise that we need. And also screen time, we know late at night is associated too with disrupting sleep. And we know there is an increase with mental health associated with less sleep too.”

Emily Underwood: “We have a question about the role of nutrition, exercise, sleep on the teen brain. What are some standout findings or what do scientists agree on at this point?”

BJ Casey: “Well, there have been several studies not only on exercise but on engagement in youth sports. And that work has shown, particularly when you’re involved in social work, that that can be a protective factor, potentially associated with lower depression. And we know that exercise increases neurotrophic factors, it feeds the brain. And so neurotrophic factors are very important in terms of plasticity, and exercise helps to increase those neurotrophic factors and plasticity in many ways. And the hippocampus is an area that’s very vulnerable to stress and very responsive to changes in neurotrophic factors. So that’s just one area and an association with the brain.”

Diana Chao: “And can I add something to that?”

Emily Underwood: “Please.”

Diana Chao: “So the two things I want to say is first, the whole concept of psychosomatic symptoms or physical manifestations of psychological distress, we often see that, and we think of it in terms of like PTSD for veterans, but it’s also manifesting in a lot of different ways for other people. So for me, my eye disease was at least partially psychosomatic, and it didn’t get better until my mental health got better. And I mention this because I really want to emphasize that mind-body connection and why everything BJ said about sleep, nutrition, exercise matters so much for your mental wellbeing.

“And I think from a practical standpoint, I know a lot of students oftentimes feel like, ‘Well, I don’t have time to exercise, I don’t have time to sleep. There’s too many things I have to do.’ And so just to give you a more actionable thing, for me, at least I try to multitask where I could, but make it make sense. So for example, if I had to read a lot of papers for school, I would use my text-to-speech converter on my phone. So then I’ll take a walk around campus, but then I’m listening to it, so then that way I can get some exercising, but then still feel like I’m doing my work. So it’s not the most ideal situation, but I just want to acknowledge that sometimes those things can feel hard to balance, but you can sneak in those little bits of multitasking there.”

BJ Casey: “And we could go on on diet. We know high fatty diets can lead to neuroinflammation and a reward circuitry that can then lead to depressed mood and also cravings for sugar, which then is this vicious cycle where you’re wanting to eat bad food and then that’s impacting your mood and mental health too.”

Emily Underwood: “I want to ask a question; this is a bit of a doozy: So does taking antidepressants when the brain is still plastic increase the risk of lifelong dependency on medication? There’s a lot to unpack there. BJ, do you want to take a first stab at this — concerns about giving teens meds, which I realize is probably very different depending on the diagnosis and the medication.”

BJ Casey: “It depends on the diagnosis, the medication, and at the point in which we diagnose someone with a mental health illness is the time in which it is disrupting the quality of life and the severity of that. And so if cognitive behavioral therapies aren’t working, medications can be helpful. And in terms of the antidepressants, I’m thinking of SSRIs that also increase neurotrophic factors, which are helpful for learning, so you wouldn’t just want to take the medication itself, you have this wonderful period of plasticity, and you’d want to work and take advantage of the coping skills and reframing of those triggers that cause that anxiety... Stimulants are example of a medication that people were concerned about. If in adolescence you gave stimulants to them to treat ADHD, would that lead to later substance abuse? And the epidemiological studies don’t support that.”

Emily Underwood: “OK, thank you. We have another great question about plasticity: Is this plasticity linked to why teens seem to change their interests on what seems like a weekly basis? What guides where the brain finally lands? And how much does early life matter in the long run? So that first piece is the plasticity why, I guess, at least some teens change their interests? As a person who also changes my interests constantly, and I’m no longer a teenager, I’m curious about that too. Go ahead.”

BJ Casey: “Yeah, so plasticity in the brain, we’re learning something new every day, and it’s also the case that often we’re living in the moment. So something that we know with the development of the prefrontal cortex is we gain the ability to think about the future as opposed to the here and now. And so I think it’s a combination of that plasticity where we’re learning and we’re having all these experiences and we’re so excited by them, and that’s in the moment. And then there’s something else that comes up that’s in the moment that we get very excited about and think less about the future. But the future is important. And every experience that we have, we carry a bit of that with us. That’s part of learning, that makes up who we are.”

Diana Chao: “I mean I’m sure a lot of it’s like a novelty thing. When something is new and exciting, it is nice. But the other thing about it is, I know for me, if I’m constantly looking for new things... And I’m sure for a lot of people it’s like a very healthy outlet, but at the same time, it could also be that you’re looking for a place to belong, you’re looking to find something that brings you joy and comfort, and you haven’t found that yet so you just keep looking at these different things. So that’s also something to think about and potentially talk about. Doesn’t mean that that is what you’re going through.”

Emily Underwood: “That’s a really wonderful observation. We have some questions about normality and then also neurodiversity, so these different ways of thinking about what’s normal. One of our guests asks, ‘My only child is 18. I’m wondering, first, how stormy is a teen mind “supposed” to be versus a diagnosable and treatable problem? And how can we know what’s normal in the wake of the pandemic and online school?’ So we’ve talked a little bit about this, the sort of how do you know, but is there anything you can add to that? BJ, do you want to take that first?”

BJ Casey: “So again, the teen brain can be a stormy but beautiful brain. And in the pandemic — already even before the pandemic — we were seeing an increase in anxiety and stress related disorders in teens. You have an 18-year-old and I just want to let you know that the emerging definition of adolescents extends into the mid-20s. And if that’s about independence from parent and caregiver, my son has told me it might extend a little bit financially beyond that time.

“I think it’s important to listen and to be supportive. And when a young person actually makes plans to do harm, when you hear messages like that, that’s when you get concerned and that’s when you really want to have resources. But it’s never a bad idea, it’s a strength, to seek out help. And so that would be my advice to everyone, for the youth and for the parent, because building mental health skills is something we could all benefit from and that’s the whole shift that I’m hoping that we move into as opposed to being reactive when there is a problem. Diana, what would you…?”

Diana Chao: “Yeah, I mean, I completely agree with that. And I think another thing is, especially with the pandemic... I mean everyone was saying like, ‘Oh, in these abnormal times, blah, blah, blah, blah.’ So I mean, we already acknowledged that it was not a normal time. So it’s also not exactly like everything’s just going to return back to the baseline we knew it to be. And that’s also not necessarily a horrible thing. It’s a new reality that we just sort of have to live with, and we have to change our perceptions of normality a little bit. And I think that also is important in terms of just not even Covid, but things like with that increased use of social media, those body-image issues where you have live video filters that can change an entire person.

“These are bringing new concerns to your mind that weren’t really a thing before, but it is what’s normal now. So if that’s what’s normal now, then we have to talk about these concerns that people are feeling in that new context. And so, like BJ said, building up skills, learning protective factors, remembering and practicing those things that bring us joy, and maybe reexposing certain scenarios in a way that feels safe, doing those things don’t have to be tied to a diagnosis. They don’t have to be pathologizing in order to be something worthwhile.”

BJ Casey: “Yes.”

Emily Underwood: “I love that.

“Well, in that spirit of not pathologizing, I would like to talk about... One of our questions is: Are there hallmarks of good mental health in teenagers?

“And maybe, BJ, from the ABCD study, there are resilience factors that have emerged. Perhaps, Diana, maybe there are things that really stand out to you when you think, ‘Wow, this is a good sign.’ You know it when you see it. What are your thoughts on that, BJ, on what some hallmarks of good mental health are in teens?”

BJ Casey: “So I’m a neuroscientist, and not a clinical psychologist, but hallmarks and, actually, skills that they need to learn... As parents, we want to protect our youth. And what’s very important is that they learn to regulate themselves and to regulate their emotions. And opportunities, so letting them fail, and opportunities to help them regulate themselves is going to set them up for a much healthier adulthood because then they’ll have those skills. So I mean, healthy is being able to let go and realize there is a tomorrow, that this isn’t the worst thing, reflecting those skills where rather than feeling devastated by failure, that leads you to actually become an expert in exactly what you failed in. And we see that in many, many anecdotal stories that I hear from young people. It’s exactly in what they failed at when they were younger that they then have formed a passion for and a career. And so giving them the opportunity so that they can explore new things and their receptiveness to that and also allowing them to regulate themselves is very important.”

Emily Underwood: “Thank you. Diana, what do you think? What does good mental health mean?”

Diana Chao: “I think definitely having a good support system, whether that be through guardians, teachers, friends, et cetera. And also just a way to have that support system within yourself too. So for example, that could be writing letters. And we talk a lot about protective factors in the Letters to Strangers guidebook, which I do recommend people check out. It’s for free on our website. It’s a whole youth-for-youth mental health guidebook. But I think the key thing is also realizing that there are going to be really hard situations, but that doesn’t mean that if we don’t have full control over them or things don’t turn out the way that we want them to, that everything ends up being the end-all be-all, that whole point of the future.

“And I know this can be very difficult because especially when you come from a very trauma-based background, one of the first things I know I felt is that numbing of the hope. And when you don’t have hope, you don’t have imagination, there is no way to create that future idea in your head for something that you can look forward to. And that’s what I hope we can use to turn around to understand as a hallmark of good mental health, a way to create that image of hope, that possibility, whether that be through role models or just conversations, so that people know that that’s something that can be regained.”

Emily Underwood: “Well, hear, hear. This conversation has made me feel hopeful. And unfortunately, we are out of time. So thank you. Thank you so much, BJ and Diana, for joining us today. And thanks to everybody in the audience and for your great questions.

“Thanks everybody for supporting Knowable Magazine, which makes these events and high-quality science coverage freely accessible to all. Thanks to the Dana Foundation for their support. This conversation, as a reminder, is going to be posted on the Knowable website. It’s going to be free to view and to share. We’ll put all these resources in one place so that you can come back to them. There’s a lot to unpack and a lot to learn more about. So please do come back and share this with others. And also, please don’t forget to fill out our survey. We really do want to hear from you about how we can make these events better and what you got out of this.

“So we will see you at our next event, on Wednesday, May 17th. And once again, BJ and Diana, I want to say thanks again for your wonderful thoughts and insights today.”

BJ Casey: “Thank you, both.”

Diana Chao: “Thank you.”