Brain MRIs reveal the impact of ‘toxic stress’ on black children

SAccording to a new study released Wednesday. The researchers found that black children were more affected than white children, largely because of the higher levels 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 area of ​​research examining how racism and other social factors can affect the physical architecture of the brain, may help explain longstanding racial disparities in the prevalence of psychiatric disorders such as PTSD.

“Even in children 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,” Nathaniel Harnett said. , an assistant neuroscientist at McLean Hospital and an assistant professor of psychiatry at Harvard Medical School, who was the study’s lead author. “If we treat the world as color blind, we’re not going to create effective mental health solutions for everyone.”

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

But linking these factors to differences in brain development – ​​which can be subtle and difficult to detect – has been difficult because of the small sample sizes in many brain imaging studies and the fact that many such studies are missing. sorely diverse, Harnett said.

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The current study took advantage of the powerful cognitive development of the adolescent brain, or ABCD, a study established and funded by the National Institutes of Health in 2015 to study the brains and experiences of approximately 12,000 American children ages 9 and 10 through early adulthood. The study includes surveys completed by parents and children as well as detailed measures of the socioeconomic characteristics of participants’ neighborhoods.

Although the ABCD study did not meet its goal of participants reflecting the US population, it is far more diverse than most studies of its type. It includes nearly 1,800 black children, which allowed Harnett’s group to probe the differences between black and white children. (Other racial and ethnic groups were not included in the study due to small sample sizes and the complexity of studying how structural racism affects different groups, said Harnett, who added that he hopes to expand his work to other 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 filled with neurons that process information — in 11 out of 14 brain areas examined. The field of psychiatry has a long history of researching and attributing differences in the brains of black people to race, but such ideas did not stand up to modern scrutiny. These claims are ridiculous in the face of the mountains of scientific evidence showing that race is a social construct and humans of different races – categories often used in research as proxies for geographic 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 low-income children in the household – both black and white. But as more black children lived in low-income households, they were more likely to be affected. The study found that up to half of the differences found in the brain volume of certain regions in black children could be attributed to social factors.

“It’s not a race effect. It’s race-related. Adversity is related to structural differences,” Harnett said. “The experiences we’ve had shape how we respond to future trauma. And these experiences are largely based on racial criteria.

The finding is “a significant contribution to our understanding of how structural inequalities evident in early development may create a pathway to increased risk of brain health disparities among Black Americans,” Negar Fani, told STAT. neuroscientist at Emory University. Her work focuses on developing targeted interventions for trauma, and she said new research suggests to her that buffers against inequality and stress – such as training, therapy or breathing exercises – should be appropriate. to specific racial and ethnic communities to be more effective.

The researchers focused on three areas of the brain critical to processing emotions and threats: the amygdala, a brain center responsible for processing frightening 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 that these areas in particular, which are strongly linked to PTSD, were smaller on average in black children and smaller in children who had experienced the most adversity. These children also had more severe symptoms of PTSD.

Harnett said he interpreted the findings as “the neuroanatomical consequences of racially disparate environments of toxic stress.” It has been discovered that toxic stress can disrupt the architecture of the developing brain by causing both too many neurons and too few neurons to be created in harmful ways. The effect of such changes, he said, may not become apparent until adulthood and may also play a role in brain aging. Another study recently showed that the black american brains may be aging faster due to the impact of racial stressors.

Perhaps as important as what the researchers found is what they didn’t find or couldn’t ask for due to study limitations, Harnett said. They looked at factors such as 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 wider range of potential stressors as the ABCD study releases more information, including data on toxins from collecting baby teeth.)

History of trauma and family conflict were not found to be associated with brain differences, but Harnett said he does not rule out that these factors may have important neurological impacts. He hopes to continue studying children as they age, looking for factors that may stop or prevent future impacts on brain development. “One of the things we hope is that these changes are malleable and could be enhanced by nurturing and increasing resources,” he said.

Deanna Barch, principal investigator of the ABCD study who wrote a editorial accompanying the new research, praised the study for raising awareness that brain differences are unrelated 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 part of the brain differences found to social factors, it could be misinterpreted as saying that race could still play a role. . “The concern is that a naïve or not-the-best-intentioned reader might flip these results around…and say that some people are fundamentally different, or less than,” she told STAT.

She said it was likely that other social factors not captured by the study could explain 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 was also concerned that research focused on deficits in brain structure could further stigmatize children who need help, but also said the research served as a call to action to provide nets. social security, health care and schools for all children. “I hate to make it seem like every child who grows up in poverty and adversity will 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 results.”

Like many fields of medicine, psychiatry has a history of ingrained racism, including abusive treatment and experimentation on people from marginalized racial groups, silence about racism, and failure to work harder to remedy it. 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 still 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 is editor of the American Journal of Psychiatry, called the findings significant, saying “they talk about the need for psychiatry”. as an arena to speak candidly about the harmful psychological impacts of race-related disparities in childhood adversity, to challenge the fact that these disparities stem from structural racism, and to vigorously support rectification efforts.

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

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