In 1844, Frederich Engels remarked in a book that the “physical effects of the living conditions of the poor had their effects from early life”. He had seen scrofula (tuberculosis of the neck), rickets, typhus, cholera, and smallpox as representative of the ways in which poverty is embodied in the bodies of the members of the working classes.
In the 1960s, neuroscientists began finding evidence that growing up poor could affect how a young brain develops. Marian Diamond, then a neuroscientist at the University of California, Berkeley, showed that rats that grew up in an “impoverished” environment had “hampered” brain development and learning abilities.
How does poverty affect the brain?
In 2015, three studies reported that human children and young adults growing up in low-income families had lower cortical volume and did relatively poorly in tests for academic performance. The cortex is the outer layer of the brain.
Together with the cortex, one of the 2015 studies focused on another area: the hippocampus. Kimberley Noble, from Columbia University, and her colleagues found that the volume of this deep-seated convoluted structure, widely regarded by scientists as the “seat for learning and memory”, correlated positively with a family’s socioeconomic status, but not parental income.
Now, a study by researchers from Harvard University and Washington University, published earlier this month in the journal Nature Communication, has demonstrated that children growing up in low-income families indeed risk a smaller hippocampus. The researchers, led by David Weissman, a postdoctoral fellow at the Stress and Development Lab, showed that generous anti-poverty policies substantially lower this risk.
The finding highlights how state-level public policies can potentially address the correlation between brain development and low income.
The study emphasises “how household finances are connected to brain development in children,” Akash Gautam, a University of Hyderabad neuroscientist who works on hippocampal development, told The Hindu. Children from low-income families might have a smaller hippocampus, which in turn might relate to later “inequities in [their] physical and mental health outcomes.”
How was the study conducted?
The relationship between brain development and low-income is relatively well-established, but the role of anti-poverty policies in this relationship is not.
The researchers used data from the Adolescent Brain Cognitive Development (ABCD) study, the “largest long-term study of brain development and child health in the United States.”
Here, the authors looked at the brain scans of over 10,000 children aged 9-11 years, located in 17 U.S. states. These states had different costs of living and anti-poverty programmes of varying generosity.
The programmes that the authors considered included two cash-assistance schemes and Medicaid, a health insurance programme.
The researchers found that the hippocampal volume was indeed larger for participants belonging to families with relatively higher income.
Impaired hippocampal development has been associated with higher risk of psychopathologies, such as major depressive disorder and post-traumatic stress disorder. So the researchers also tested the relationship between family income and the incidence of internalising (e.g. depressive disorders, anxiety, etc.) and externalising psychopathologies (e.g. drug abuse, violent behaviour, etc.) in children.
They found that family income was “negatively associated” with the incidence of these psychopathologies: higher the family income, lower the incidence of internalising and externalising psychopathologies in the children.
The authors noted that the strengths of these associations varied across the 17 states where the data was available, so they found out whether the costs of living and anti-poverty policies in these states could influence these associations.
“We observed a three-way interaction between family income, cost of living, and generosity of cash assistance programs in predicting hippocampal volume,” the paper stated. If one were living in a low-income household in a state with a higher cost of living, and received generous cash benefits, their hippocampal volumes were, on average, 34% larger than those who lived in low-income households in states with a relatively higher cost of living and lower cash benefits.
Similarly, the authors found that for children growing up in low-income households, “more generous cash benefits are associated with greater reductions in internalising problems”.
So the study found that poverty could shape biological properties, like brain development, and highlighted the role governments and public policy could have in ameliorating the biological effects of poverty.
Did the study have any shortcomings?
Poverty is often a symptom of more systematic discrimination. For example, in 2007-2011, American Indians, Alaska Natives, and African-Americans had the highest poverty rates in the U.S. Similarly, in India, communities listed as Scheduled Tribes (STs), Scheduled Castes (SCs) and Other Backward Classes (OBCs) are significantly poorer than those not listed in these categories, according to a recent study.
So, what if the patterns the study uncovered were not due to poverty but due to racism? In an email to The Hindu, Dr. Weissman agreed to the possibility, adding that they tried to rule out as many alternative explanations as possible, including racial and ethnic makeup of the sample, using supplemental analyses.
“The results held consistently across these analyses,” he said, adding that the results may not be directly applicable in India, because the “macroeconomic conditions in India are very different”.
However, Dr. Weissman said that their findings supported something “intuitive” that could be generalisable, “that policies or economic conditions that have a direct influence on a family’s financial resources matter for children’s brain development.”
The study also worked with the ABCD database, which allowed them to sample brain scans only from 17 out of the 50 U.S. states. Rohan Sarkar, a PhD scholar at the Indian Institute of Science Education and Research, Kolkata, said that despite the dataset being broader than in previous studies, the data being limited to 17 states limited the “power of the inference provided”.
How can anti-poverty policies help?
Mr. Sarkar and Dr. Gautam both said that the relationship between socioeconomic status and hippocampal development might not be “so simple”. According to Dr. Gautam, while hippocampal size is correlated to cognitive development and the incidence of psychopathologies, a smaller hippocampus wouldn’t necessarily indicate that “a child will experience significant impairments in these areas”.
“The brain is a complex and adaptable organ, and compensatory mechanisms can sometimes mitigate these effects,” he added.
According to the new paper, more generous anti-poverty policies could “amplify or reduce stressors associated with low income”. That is, having access to more financial resources could “shield families from experiencing some of the chronic stressors associated with low income that can influence hippocampal development”.
Finally, ‘generous’ anti-poverty policies don’t just increase family income; they can also allow “families to make decisions that lead to a decrease in wages but that also reduce stress, such as working fewer hours,” per the new paper.
What is the study’s future?
The authors of the current paper worked with data collected in 2017-2018. But according to Dr. Weissman, its youth participants have returned every year, allowing the researchers to study how “policy changes that have occurred since these data were collected … has influenced the trajectories of the youth’s mental health and brain development”.
The study also illustrated how “investments in social safety net programs” could lower the high cost of “addressing mental health, educational, and economic challenges resulting from socioeconomic disparities in neurodevelopment” tomorrow.
Sayantan Datta (they/them) are a queer-trans freelance science writer, communicator and journalist. They currently work with the feminist multimedia science collective TheLifeofScience.com and tweet at @queersprings.