JOHN YANG: Childhood trauma can have lasting psychological effects.

Now Laura Barron-Lopez reports that a new study has found that early childhood stress from things like poverty and trauma can actually change the structure of children's developing brains.

LAURA BARRON-LOPEZ: For this study, researchers at Harvard analyzed thousands of MRI brain scans of children ages 9 and 10.

They were able to identify small physical changes in children facing higher levels of adversity.

These changes could play a role in mental health issues later in life.

They concluded that Black children are more likely to be affected.

Nathaniel Harnett is a neuroscientist at McLean Hospital and an assistant Professor of Psychiatry at Harvard Medical School.

He's the study's senior author.

Nathaniel, thanks so much for joining us.

How did you identify the children facing adversity in this study?

NATHANIEL HARNETT, Neuroscientist: Thanks for having me.

We looked at indices of adversity for participants that participate in the Adolescent Brain and Cognitive Development Study.

This is a multisite led longitudinal study happening across the United States.

We looked at things like neighborhood disadvantage, how much resources that the kids had in their neighborhoods, levels of family conflict, fighting within the home, and things like material hardship, how hard it is to put food on the table.

When we looked at those variables, we really saw that over and above, black children in the sample had much more exposure to adversity than White children in the sample.

LAURA BARRON-LOPEZ: And so then you specifically looked at the MRI brain scans of, as you said, Black and White children, and what did those scans reveal?

NATHANIEL HARNETT: So, we looked at MRI scans, and we looked particularly at brain regions that are involved in emotion, helping us regulate our response to potentially threatening events in our environment.

We think that these brain regions are important for psychiatric disorders like posttraumatic stress disorder.

And when we look at those brain regions, when we compare White and Black children exposed to different levels of adversity, we see that Black children have relatively smaller volume of these different brain regions compared to White children.

These are massive differences, but they are significant.

Part of what we worry about is how those might change over time as these kids get older and contribute to other mental health disorders.

LAURA BARRON-LOPEZ: And it was a lower volume of gray matter, correct?

NATHANIEL HARNETT: Yes, it was lower volume of gray matter.

LAURA BARRON-LOPEZ: And so, specifically, when you say that, that impacts black children more, what does that translate to in their lives?

NATHANIEL HARNETT: It's hard to say exactly from this study what that translates to.

But we know from the literature that lower gray matter volume in regions like the prefrontal cortex, like we saw here, are associated with, again, psychiatric disorders like PTSD, depression, and anxiety.

And so, as these kids continue in the study, as we look at what happens to their brains later on, part of what we might see, and part of what were we might see, is an increased incidence of these psychiatric disorders.

LAURA BARRON-LOPEZ: And was racism at all one of the stressors that you looked at, or the impact of racism on these children and their brains?

NATHANIEL HARNETT: We looked at indices of structural racism in this study, so we looked at things that are impacted by socio and historical decisions that have been made that disproportionately affect black children and other racially minoritized children.

Part of the reason we didn't look at racial discrimination is we didn't have data from when the kids were 9 to 10.

We only had that data as they got older.

So, it's difficult really to say what the influence of racial discrimination might have been here, but we're hoping to look at that in the future.

LAURA BARRON-LOPEZ: And are these changes reversible, the changes that were made in these children's brains?

And what do you think policymakers could do to fix it?

NATHANIEL HARNETT: I think the fact that the differences we see are so small indicate that they are potentially reversible and that by increasing the amount of resources that parents have that these children have access to, by improving their neighborhoods, those are the types of things that we think at a structural level could benefit all kids.

Not just black children, but white and black and really help to reverse these damages that we see.

As a neuroscientist, it's hard to come up with policy decisions, but I think anything that's really going to help diminish the structural inequities that we see that are having real impacts on these children is going to beneficial.

LAURA BARRON-LOPEZ: What limitations do you think presented itself in this study and what do we know about the impact on potentially other ethnicities?

NATHANIEL HARNETT: I think one of the major limitations is one that you've hinted at and that we only looked at black and white show in this study.

These again, it's a relatively restricted rate range.

They're only about 9 to 10 years old.

And so we really want to look and see at earlier ages, at further out ages, what might be happening over time.

Because of the way that racism and structural racism can interact differently for separate racial and ethnic groups, we really want to bring on more researchers with expertise in these areas before we go digging around and try to figure out what's happening there.

LAURA BARRON-LOPEZ: One of the things that you wanted to do in this research was to dispel this idea, this folk belief that black and white people have different brains.

Do you feel like you accomplish that?

NATHANIEL HARNETT: I feel like we've contributed to that literature in a positive way.

I think, as you've noted, there seems to be this idea that people are essentially different.

And I think what we're really showing here is that a really huge part of what's different between black and white kids is that they're exposed to disproportionate burden of adversity.

It's really hard for everyone to be playing on the same field and having these same outcomes when the game is rigged against some people.

LAURA BARRON-LOPEZ: Nathaniel Harnett, thank you so much for your time.

NATHANIEL HARNETT: Thank you for having me.