A new article published in JAMA Network Open finds that childhood poverty is linked to increased instances of externalizing problems (dysfunctional behaviors directed outward, such as violence) as well as reduced cortical surface area in numerous brain regions. However, the current research found no such connection for internalizing problems (dysfunctional thoughts and attitudes directed inward, such as depression).
According to the authors, the association between poverty and externalizing problems is partially explained by the observed reduction of brain volume. They write:
“The findings of this study suggest that childhood poverty is associated with increases in externalizing problems, but not internalizing problems, over time in early adolescence. This association is mediated by reductions in the cortical surface area across numerous brain regions. These findings highlight potential neurobiological mechanisms underlying the link between poverty and the emergence of externalizing problems during early adolescence.”
The current work investigates the connections between poverty, internalizing and externalizing problems, and adolescent brain mass. The authors used data collected during the Adolescent Brain Cognitive Development (ABCD) Study, the most extensive study to collect longitudinal data on children’s brain development in the United States. Seven thousand five hundred sixty-nine children aged 9 to 10, and their parents, provided data for a baseline measure between September 2016 and October 2018, as well as a one-year follow-up.
The current work only included participants from the ABCD study that underwent a magnetic resonance imaging (MRI) assessment and provided data on poverty (as defined by the US Department of Health and Human Services), psychopathological symptoms (as measured by the Child Behavior Checklist), child age, sex, race, ethnicity, and parent’s level of education. 55.7% of the participants were white, 47.5% were girls, and 13.8% lived below the poverty line in 2016 and 2018.
Poverty was associated with greater externalizing problems at both the baseline and 1-year follow-ups. Participants above the poverty threshold had a mean externalizing score of 4.02 for the baseline measure, compared to 6.34 for those below the poverty line. The one-year follow-up showed similar results, with those above the poverty line having a mean externalizing score of 3.82, compared to 5.99 for those below the poverty line.
Internalizing problems were similar for the baseline measure (5.01 versus 5.89) and the 1-year follow-up (5.20 versus 5.54) for both groups, indicating little association with poverty. However, the authors note that internalizing problems often appear later in adolescence and young adulthood and so may not have been captured in the current research. Additionally, the present work finds that internalizing problems associated with poverty decrease as children age while externalizing problems increase.
Further, poverty was associated with less cortical surface area in several parts of the brain, including those involved in auditory and language processing, visual recognition and processing, and executive function and decision-making. Poverty was also associated with reduced cortical volume. The authors estimate that differences in cortical surface area and volume mediated 9% of externalizing behaviors in participants living beneath the poverty line.
In other words, the authors estimate brain differences likely caused 9% of externalizing behaviors, a non-trivial number considering the numerous factors involved in externalizing behaviors (genetic, familial, and social factors, for example).
The authors acknowledge several limitations to the study. First, poverty and brain structure were measured simultaneously. The current work did not examine brain changes over time. Other forms of adversity, such as abuse, were not measured. The psychopathological data was provided by parents and could have looked different if provided by the participants themselves.
The present study only looked at adolescents and is not generalizable to other populations. Additionally, the participants were majority white, and many of their parents had attained postgraduate degrees (37.2% in the study versus about 13% in the US population), further limiting generalizability.
The authors conclude:
“The finding in this study that structural brain differences may mediate the association between poverty and elevated externalizing problems underscores the importance of attention to public health programs policies that target early intervention and prevention. Future work should use longitudinal neuroimaging data to examine the association between poverty, developmental trajectories of cortical structures, and psychopathologic factors.”
In line with the current research, previous research has found no brain differences in people that struggle with depression. Researchers have criticized small-scale brain imaging studies for inflating effect sizes and presenting a false narrative. MRI experts have also condemned brain scan studies as “problematic” and likely “unsubstantiated.” A large study with over 21,000 participants found that brain scans cannot differentiate between mental health conditions.
Research has found that an influx of financial resources promotes infant brain activity. Conversely, poverty likely affects the brain’s executive functioning and decreases activity in the prefrontal cortex. One study found that impoverished children’s activity in the prefrontal cortex resembles that of stroke victims. Studies have also linked smaller brain size and neurological impairment to childhood poverty. Poverty rates can also predict youth suicide risk in the United States.
Kim, H. H., McLaughlin, K. A., Chibnik, L. B., Koenen, K. C., & Tiemeier, H. (2022). Poverty, cortical structure, and Psychopathologic characteristics in adolescence. JAMA Network Open, 5(11). https://doi.org/10.1001/jamanetworkopen.2022.44049 (Link)