Researchers have long observed that children growing up in poverty are at greater risk for cognitive and psychological delays. These early difficulties continue to hinder normal growth throughout childhood and into adulthood, potentially leading to lower academic achievement and perpetuating disadvantage into subsequent generations.
To understand the deep physiological basis for poverty and brain development, researchers have turned to the burgeoning field of brain imaging.
A recent study appearing in the online journal PLOS One uses data from a multi-site brain imaging study to compare the amount of gray matter in the hippocampus of poor and non-poor children. The hippocampus is the region of the brain associated learning and memory that is known to be affected by stress. Growing up in an impoverished environment might produce enough of the stressors to disrupt the normal development of the hippocampus. In animal studies, low levels of stress and the availability of enriching environments have been found to promote the development of the hippocampus and to increase resiliency by increasing neuronal cells.
The authors classify income into nine categories, and find that a one point increase in the income score is associated with an overall increase of .14 standard deviations in the concentration of beneficial gray matter in the hippocampus (results are similar looking at total hippocampus, and the left and right hemispheres separately). The authors find no association between income and whole-brain volume, however. Because the study screened out children with severe developmental delays and mental health conditions these results likely understate the overall impact of poverty on hippocampus development.
A Policy for Better Brains?
Much has been made of the importance of intervention targeting the brains of very young children, including the landmark National Academies report “From Neurons to Neighborhoods,” and if the hippocampus is implicated in this early development than the study further strengthens the case for improving the quality of day care and early parenting. Yet it remains unclear how to measure all of the inputs to brain development, including income, which is surely more a proxy than a direct cause of brain development. Policymakers are still searching for the optimal mix of inputs to promote brain development in children, and perhaps just as importantly, to sustain that development over the life course.
There is also some danger in making too big of a deal of the differences in the brains of poor and non-poor people, even if the intention is to highlight the damaging role of deprived environments. Research such as this study highlights a tension among scholars that study the psychological basis of poverty between showing that the poor possess the same mental capacities and emotional resources as the non-poor but operate under more constraints that predictably cause them to make bad decisions, and those that emphasize the underlying cognitive and emotional stresses that eventually “get under the skin.” For better or worse, we lack a discourse that can make a clear moral and conceptual distinction between the distressed environment and the brain that is caused by it.