MRI scans reveal disparate impact of poverty and other ‘toxic stress’ on brains of Black children

Stressful experiences during early childhood — particularly economic strife — appear to act as a toxic stressor that can alter regions of the brain tied to the processing of stress and trauma, according to a new study published Wednesday. The researchers found that Black children were impacted more than white children, largely because of the higher amounts of poverty and adversity they face.

The researchers analyzed MRI scans to identify small differences in the volume of certain brain structures, and said these could accumulate as children age and play a role in the later development of mental health problems. The finding, part of an emerging research field looking at how racism and other social factors may affect the physical architecture of the brain, may help explain longstanding racial disparities in the prevalence of psychiatric disorders such as PTSD.

“Even in kids as young as 9 to 10 years old, the disparities faced by certain groups of people have a clear impact on how the brain develops in areas that can lead to trauma and stress-related disorders such as PTSD,” said Nathaniel Harnett, an assistant neuroscientist at McLean Hospital and an assistant professor of psychiatry at Harvard Medical School, who was the study’s senior author. “If we’re going to treat the world as colorblind, we’re not going to create mental health solutions that are effective for all people.”

As many studies, including the current one, confirm, Black children in America experience more adversity than white children due to deep and historical structural inequalities. Caregivers of white children in the study were three times more likely to be employed and far more likely to have higher education levels and annual incomes above $35,000. Black children in the study were more likely to experience traumatic events, family conflict, and to live in poorer and more violent neighborhoods.

But tying such factors to differences in brain development — which can be subtle and hard to detect — has been difficult because of small sample sizes in many brain imaging studies and the fact that many such studies are sorely lacking in diversity, Harnett said.

The current study took advantage of the powerful Adolescent Brain Cognitive Development, or ABCD, study established and funded by the National Institutes of Health in 2015 to study the brains and experiences of roughly 12,000 American 9- and 10-year-olds through early adulthood. The study includes surveys filled out by both parents and children as well as detailed metrics on the socioeconomic characteristics of participants’ neighborhoods.

While the ABCD study did not reach its goal of participants mirroring the American population, it is far more diverse than most studies of its kind. It includes nearly 1,800 Black children, which allowed Harnett’s group to probe for differences between Black and white children. (Other racial and ethnic groups were not included in the study because of the smaller sample sizes and the complexities of studying how structural racism affects different groups, said Harnett, who added that he hopes to expand his work to additional groups, including people who are mixed-race, as he is, in the near future.)

By analyzing brain scans, the researchers found that Black children had a lower volume of gray matter — regions packed with neurons that process information — in 11 of 14 brain areas examined. The field of psychiatry has a long history of searching for and attributing differences in the brains of Black people to race, but such ideas have not held up under modern scrutiny. These claims are ridiculous in the face of mountains of scientific evidence showing that race is a social construct and humans of different races — categories often used in research as proxies for geographical ancestry — share 99.9% of their DNA. The new study provides evidence that further refutes this discredited notion.

The new analysis, published in the American Journal of Psychiatry, found that disparities in eight of 14 brain areas were affected by childhood adversity, particularly low household income. The study found lower brain volume in these areas in children with lower household income — both Black and white. But since more Black children lived in lower-income households, they were more likely to be impacted. The study found that up to half of the differences found in the volume of the brains of some regions in Black children could be attributed to social factors.

“This is not a race effect. It’s race-related. The adversity is related to structural differences,” Harnett said. “The experiences we’ve had shape how we respond to future trauma. And these experiences largely fall along racial lines.”

The finding is “a tremendous contribution to our understanding of how structural inequities evident in early development can create a pathway to increased risk for brain health disparities in Black Americans,” Negar Fani, a neuroscience researcher at Emory University, told STAT. Her work focuses on developing targeted interventions for trauma, and she said the new research suggests to her that buffers against inequities and stress — like training, therapy, or breathing exercises — should be tailored to specific racial and ethnic communities to be more effective.

The researchers focused on three areas of the brain critical to processing emotion and threat: the amygdala, a brain center responsible for processing fearful and threatening stimuli; the hippocampus, which plays a major role in learning and memory; and the prefrontal cortex, which regulates responses to fear. They found these areas in particular, which are closely linked to PTSD, were smaller on average in Black children and smallest in those children that had experienced the most adversity. These children also had more severe symptoms of PTSD.

Harnett said he interprets the findings as “the neuroanatomical consequences of racially disparate environments of toxic stress.” It’s been found that toxic stress can disrupt the architecture of the developing brain by causing the creation of both too many neurons and too few in harmful ways. The effect of such changes, he said, may not become apparent until adulthood, and may also play a role in how the brain ages. Another study recently showed that the brains of Black Americans may age faster due to the impact of racial stressors.

Perhaps as important as what the researchers found is what they did not find, or were not able to ask because of limitations of the study, Harnett said. They examined factors like neighborhood-level pollution and family conflict, for example, but did not include nutrition, or direct exposure to toxins. (Future studies may be able to probe a broader spectrum of potential stressors as the ABCD study releases more information, including toxin data from the collection of baby teeth.)

Trauma history and family conflict were not found to be associated with brain differences, but Harnett said he did not rule out that those factors could have important neurological impacts. He hopes to continue to study the children as they age, searching for factors that may stop or prevent future impacts to developing brains. “One of the things we’re hopeful for is that these changes are malleable and could be ameliorated by nurturing and more resources,” he said.

Deanna Barch, a principal investigator with the ABCD study who wrote an editorial accompanying the new research, praised the study for raising awareness that brain differences are not tied to race.

But Barch, a professor of psychological and brain sciences at Washington University in St. Louis, said she was concerned that because the study attributed only some of the brain differences found to social factors, it could be misinterpreted as saying race could still play a role. “The concern is that a reader who is naive or doesn’t have the best intentions could flip these results upside down … and say some people are fundamentally different, or less than,” she told STAT.

She said it was likely that other social factors not considered by the study could account for the brain differences, such as the direct effects of racism and school quality, and interactions between factors such as family income, material hardship, and neighborhood safety.

Barch said she also worried that research focusing on deficits in brain structure could further stigmatize children who need help but also said that the research serves as a call to action to provide social safety nets, health care, and schools for all children. “I hate to give the impression that every kid who grows up in poverty and adversity is going to have a bad outcome because that’s not true,” she said. “But let’s not kid ourselves that these things don’t lead to bad outcomes.”

Like many areas of medicine, psychiatry has a history of entrenched racism, including abusive treatment and experimentation on people from marginalized racial groups, staying silent about racism, and not working harder to address wide disparities in access to mental health care. The American Psychiatric Association apologized for its role in structural racism in 2021, but some leaders in the field say the new study shows there is more work to be done.

Ned H. Kalin, who chairs the department of psychiatry at the University of Wisconsin School of Medicine and Public Health and serves as editor in chief of the American Journal of Psychiatry, called the findings critically important, saying “they speak to the need for psychiatry as a field to be outspoken about the detrimental psychological impacts of race-related disparities in childhood adversity, to call out the fact that these disparities stem from structural racism, and to vigorously support rectifying efforts.”

This is part of a series of articles exploring racism in health and medicine that is funded by a grant from the Commonwealth Fund.

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