Socioeconomic Status Linked to Child’s Brain Size

VBCN - May 2015 Volume 2, No 1

In the largest study of its kind, a team of neuroscientists concluded that socioeconomic adversity affects brain development in children. Children in the lowest socioeconomic strata had significantly smaller brain surface area than children from more well-off parents, as reported in the multicenter study led by Kimberly Noble, MD, PhD, of Columbia University, New York (Noble KG, et al. Nat Neurosci. 2015;18:773-778).

Dr Noble and colleagues recorded brain images of 1099 children, adolescents, and young adults in several US cities. Because individuals with lower incomes are more likely to be from minority ethnic groups, they also mapped each child’s genetic ancestry, and adjusted the calculations so that the effects of poverty would not be skewed by small differences in the brain structure among various ethnic groups.

“To the best of our knowledge, this is the first study of socioeconomic status and the brain to include as covariates continuously varying measures of degree of genetic ancestry,” the authors explained.

In children from the poorest families, income disparities of only a few thousand dollars were associated with major differences in brain structure, particularly in areas associated with language and decision-making skills. Children’s scores on tests measuring cognitive skills, such as reading and memory ability, also declined as parental income dropped. Specifically, the brains of children from the lowest income brackets (ie, annual family income of less than $25,000) had up to 6% less surface area than brains of children from families with incomes exceeding $150,000. The authors suggested that the logarithmic association between family income and surface area implies “that for every dollar in increased income, the increase in children’s brain surface area was proportionally greater.” The association was steepest at the lowest end of the income spectrum.

Family income was significantly associated with surface area in widespread regions of children’s bilateral frontal, temporal, and parietal cortices as well as right occipital cortex. Relationships were strongest in bilateral inferior temporal, insula, and inferior frontal gyrus, and in the right occipital and medial prefrontal cortex—regions linked to language and executive function. Income was also significantly correlated with 4 cognitive assessments from the US National Institutes of Health Toolbox Cognition Battery. Furthermore, parental education was linearly associated with total brain surface area, independent of age, scanner site, sex, and genetic ancestry factor. Education was also positively correlated to the left hippocampal volume.

The factors driving these differences are unclear, but could include differences in the prenatal environment or ongoing disparities in postnatal experience and exposures, such as family stress, cognitive stimulation, environmental toxins, or nutrition.

In their discussion of the findings, Noble and colleagues cautioned, “Our results should in no way imply that a child’s socioeconomic circumstances lead to an immutable trajectory of cognitive or brain development.”

They hope that “by elucidating the structural brain differences associated with socioeconomic disparities, we may be better able to identify more precise endophenotypic biomarkers to serve as targets for intervention, with the ultimate goal of reducing socioeconomic disparities in development and achievement.”

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