Differences in Brain Structure Linked to Social Disadvantage

Batya Swift Yasgur, MA, LSW

February 09, 2023

Brain volume disparities among young children of different races may be due to adverse childhood experiences related to socioeconomic conditions and structural racism, new research suggests.

Investigators from the Belmont, Massachusetts-based McLean Hospital, an affiliate of Mass General Brigham, found that nine- and 10-year-old children of different racial and socioeconomic backgrounds have subtle neurobiological differences in gray matter volume in certain brain regions associated with trauma and stress.

Lead investigator Nathaniel Harnett, PhD, assistant professor of psychiatry at Harvard Medical School, Boston, Massachusetts, believes this research shows evidence that "structural racism" — broad socioeconomic disadvantages that lead to poverty and emotional trauma — may affect brain structures and growth and ultimately may lead to psychiatric illness.

"For clinicians, I think the take-home message is that we really need to be more aware about the ways in which the disproportionate burden of stress might impact some groups," Harnett told Medscape Medical News.

"This in turn can affect the way they respond either to later stress or maybe even treatment outcomes." He added that other brain regions and compensatory mechanisms are likely to be involved, and more work needs to explore these connections.

The study was published online February 1 in The American Journal of Psychiatry.

'Toxic Stressor'

Harnett and colleagues used MRI and survey data from the 2019 Adolescent Brain Cognitive Development (ABCD) study involving over 12,000 children from 21 sites across the US.

Participating children provided information about emotional and physical conflicts in the household. The ABCD study also surveyed the parents about their race and ethnicity, parental education, employment, and family income. Another factor in the analysis was neighborhood disadvantage, based on the Area Deprivation Index utilizing 17 socioeconomic indicators from the US Census, including poverty and housing.

Comparing brain MRI findings from approximately 7300 White children and 1800 Black children in the ABCD study, Harnett’s group found that Black children had lower gray matter volume in the amygdala, hippocampus, and other subregions of the prefrontal cortex.

Experience of adversity was the "sole factor" explaining brain volume differences, with household income being the predominant factor.

Compared with White children, Black children were three times less likely to have parents who were currently employed. In addition, White parents were more likely than Black parents to have higher education at 75.2% vs 40.6%. Black families had significantly lower household income than White families and experienced more family conflict, material hardship, neighborhood disadvantage, and traumatic events.

The researchers analyzed race-related differences in posttraumatic stress disorder (PTSD) symptoms and the relationship with adversity and found that Black children had significantly greater PTSD symptom severity, and that symptom severity was "further predicted by adversity."

"Taken together, early-life adversity may act as a toxic stressor that disproportionately impacts Black children as a result of their significantly greater exposure to adversity and contributes to differential neural development of key threat-processing regions," the investigators write.

"These parts of the brain are involved in what we typically call threat learning," Harnett explained. "Threat learning is basically learning to recognize potential dangers in our environment and selecting behaviors to keep us safe, whether we're going to run away from a danger or face it head on. When you have chronic exposure to things that can be dangerous or can make you feel unsafe, that might have an impact on how these brain regions develop, with potential implications for how these regions function later on in life."

A Consequence of Toxic Stress

This study is part of a growing body of work on the influence of "toxic stress" and other forms of PTSD on brain architecture. The authors note that prolonged exposure to adverse experiences leads to excessive activation of stress-response systems and accumulation of stress hormones. This disrupts immune and metabolic regulatory systems that influence the developing structures of the brain.

The study helps to contradict the "pseudoscientific falsehood" of biologic race-related differences in brain volume, instead emphasizing the role of adversity brought on by structural racism, the authors add.

In an accompanying editor's note, The American Journal of Psychiatry Editor-in-Chief Ned H. Kalin, MD, called childhood adversity, maltreatment, and stress, "significant risk factors for the development of psychopathology."

These findings are "critically important, as 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 by pursuing policy changes," he stated in a news release.

Social Construct?

Commenting for Medscape Medical News, Joan Luby, MD, coauthor of an accompanying editorial, said she and her coauthor "really appreciate the study and think the findings are overall very consistent with the emerging literature, increasing the confidence [in the findings]."

Luby, a professor of child psychiatry and director of the Early Emotional Development Program, Washington University School of Medicine, St. Louis, Missouri, noted that she "takes issue" with the fact that the study "makes inferences regarding race, when we think those inferences aren’t well justified, are misinterpretations, and could be misleading."

Race is a "social construct" and there are many sources of adversity that the authors didn’t measure in the study and are likely the source of any remaining variance they found, including experiences of structural racism and discrimination," said Luby, who was not involved in the study.

"How people look doesn’t have any bearing on their inherent biological characteristics, and more [needs to be studied] on how they experience the psychosocial environment and how the psychosocial environment rejects or reacts to them."

These psychosocial issues "have to be taken into account and measured in a very comprehensive way," she added.

The ABCD study was supported by the NIH and additional federal partners. Harnett reports no relevant financial relationships. The other authors’ disclosures are listed on the original paper. Luby receives royalties from Guilford Press. Her coauthor reports no relevant financial relationships.

Am J Psychiatry. Published online February 1, 2023. Full text; Editor's Note; Editorial.

Batya Swift Yasgur, MA, LSW, is a freelance writer with a counseling practice in Teaneck, New Jersey. She is a regular contributor to numerous medical publications, including Medscape and WebMD, and is the author of several consumer-oriented health books as well as Behind the Burqa: Our Lives in Afghanistan and How We Escaped to Freedom (the memoir of two brave Afghan sisters who told her their story).

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