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Topics: Diversity & Inclusion, Five Questions

Neuroimaging Links Structural Racism to Brain Changes, PTSD

Five Questions with Nathaniel Harnett on his two-year fellowship with Harvard Catalyst.

Nathaniel Harnett in an aerial silks class.
Nathaniel Harnett in an aerial skills class.

Nathaniel Harnett, PhD, didn’t set out to dispel a lingering myth that the brains of Blacks and Whites are fundamentally different. His focus was on untangling the brain basis of post-traumatic stress disorder (PTSD).

Then his research team found subtle but telling differences in the stress-response systems of Blacks compared to Whites that showed up as early as 9 or 10 years old. The results suggest that what’s different about the brains of Black people is that they’re exposed to a disproportionate burden of adversity in childhood.

The headline-making findings have opened some fundamental questions about the relevance of current neuropsychiatric models to historically marginalized populations and added a new layer of complexity to the evolving narrative around ethnic differences in the brain.

Harnett, assistant professor of psychiatry at Harvard Medical School and assistant neuroscientist at McLean Hospital, was awarded our two-year faculty fellowship (2022-24) in diversity inclusion to further his research.

You’re midway into the research fellowship. How does that intersect with your career in translational science?

The Harvard Catalyst faculty fellowship supports junior scholars and faculty in research endeavors that are likely to lead to future funding. It frees up time to do the kind of work that we want to focus on in the future and provides training in methods and topic areas that we might not otherwise have time for.

“Can we use our understanding of PTSD to truly help people?”

My project is trying to understand the neurobiological effects of early-life stress, which disproportionately burdens underrepresented populations, and the impact this has on one’s response to later traumatic events. Can we use our understanding of PTSD to truly help people?

The fellowship allows me to conduct basic scientific research on the disorders that I’m interested in as a psychiatric researcher and determine whether this is translatable. Is it something that we’re able to generalize to other people? Can we use this as a basis to alleviate or diminish the prevalence of PTSD and other trauma-related disorders in the future?

What led you to this area of research?

I have always been interested in understanding the brain basis of PTSD. Two people are involved in a car accident; one of them goes on to develop PTSD and one of them doesn’t. What is the brain mechanism that’s driving that particular difference? How do people respond to threats? How does that relate to future responses?

We’ve done a lot of work in trying to figure out the neural circuitry around these questions, but the story gets a little messy when you start breaking down the group results.

We have found different neural phenotypes associated with PTSD in Black and other racially and ethnically minoritized groups, and further, that the socioeconomic burdens and social pressures these groups face is directly impacting the neurobiology related to PTSD. Now we want to apply this knowledge to those who are directly affected.

My research raises the issue of generalizability in neuropsychiatric models, because if our models of brain disorders are not true for all groups, their usefulness in the general population is likely to be limited. It also compels us to consider what’s happening when we expose people to the consequences of the social and historical racism that has been ingrained in this country since its inception. Those are really important issues to me that have driven this work.

I never set out to focus on development, but we’re talking about children. We found brain changes in 9- and 10-year-olds. They don’t have a choice in where they’re born or what their parents did. What they’ve had to endure growing up in this environment is not the same as others, yet society expects them to be like everyone else. That has always bugged me.

How does your work inform common misperceptions about structural brain differences among ethnicities?

I think we often speak colloquially about essential differences between people without realizing we’re doing it. How some people just behave a certain way, or something is ingrained in their genes, or maybe that Black people are more prone to this and White people are more prone to that. Many times we end up reifying those ideas about racial and ethnic groups, when in reality, everything we’ve learned shows that it’s the totality of our experiences throughout development that inform our later behaviors.

“Our studies show very clear differences in the environments these kids are growing up in and the impact of that on the brain.”

We’ve known for a long time that trauma, maltreatment, or adversity in childhood can set you up to respond differently to a trauma in adulthood that might then lead to PTSD. Yet we don’t often think about racial and ethnic variability in that pathway.

Our studies show very clear differences in the environments these kids are growing up in and the impact of that on the brain. The regions affected are important for emotion regulation, learning to respond to threat, and understanding you’re in a safe environment, all of which are tied to PTSD. For example, we’ve seen blunted reactivity to threat in Black adults compared to Whites, which is completely driven by differences in neighborhood disadvantage and the amount of violence they’re exposed to in developing years.

So we have this developmental trajectory in which young people who are exposed to the consequences of racism in this country end up having changes in brain regions that are really important for how they’re going to respond to stress later in life. If we really want to develop effective, generalizable treatments for these psychiatric disorders, we ought to keep that in mind.

What is the end goal of this work?

The goal of my lab is to develop effective neuroscience-based interventions for trauma and stress-related disorders.

Understanding the impact of racial inequities on the brain and on treatment responses is a core part of making sure that the models of psychiatric disorders we’re working with are available to those most in need. I think it’s also important to audit what’s already been done in that regard, to make sure that interventions aren’t based on models that are not representative of the population, because they might not work across all groups.

To me, this research is about making sure that we’re taking a holistic approach to the understanding of psychiatric disorders, and really keeping in mind the people that we’re trying to serve.

You’ve co-authored nearly 30 papers on these topics in the last two years alone. How do you find work/life balance in the midst of this?

I think I’ve figured out a few things to help with work/life balance, now that I better understand that time is limited and fleeting, and you should make the most of it. I started playing music again, and am teaching myself keyboard. I started taking aerial silks classes with some friends.

I try to make sure that I’m taking as much time off as I’m working, because I know that feeling–and I feel it now–of being just completely burnt out. What is the point of studying how other people respond to stress and go on to develop psychiatric disorders, if you’re going to put yourself in all this stress and then go on to develop a psychiatric disorder?

You can’t pour from both ends. If you want to help the most people, you have to take care of yourself.  I’m trying to embrace that as best I can.

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