Income inequality, gene expression, and brain maturation during adolescence

Abstract

Income inequality is associated with poor health and social outcomes. Negative social comparisons and competition may involve the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes in underlying some of these complex inter-relationships. Here we investigate brain maturation, indexed by age-related decreases in cortical thickness, in adolescents living in neighborhoods with differing levels of income inequality and household income. We examine whether inter-regional variations relate to those in glucocorticoid receptor (HPA) and androgen receptor (HPG) gene expression. For each sex, we used a median split of income inequality and household income (income-to-needs ratio) to create four subgroups. In female adolescents, the high-inequality low-income group displayed the greatest age-related decreases in cortical thickness. In this group, expression of glucocorticoid and androgen receptor genes explained the most variance in these age-related decreases in thickness across the cortex. We speculate that female adolescents living in high-inequality neighborhoods and low-income households may experience greater HPA and HPG activity, leading to steeper decreases in cortical thickness with age.

Figure 1

Mean cortical thickness by age in male and female income (low, high) groups. Within each income group plot inequality subgroups are stratified: high = solid circles and solid line, low = hollow circles and dashed line. In predicting cortical thickness, the interaction between age by inequality was analyzed for each male and female income group.

Figure 2

The y-axis (Cortical Thickness by Age) is the Fisher z-transformed correlation coefficients of cortical thickness and age in each of the 34 regions. The x-axis is the NR3C1 expression in each of these regions. For each subgroup, there are 34 points representing each cortical region. Each male and female income subgroups are divided into high (solid circle, solid line) and low (hollow circle, dashed line) inequality subgroups. An inequality by NR3C1 expression interaction was analyzed for each income group.

Figure 3

The y-axis (Cortical Thickness by Age) is the Fisher z-transformed correlation coefficients of cortical thickness and age in each of the 34 regions. The x-axis is the AR expression in each of these regions. For each subgroup, there are 34 points representing each cortical region. Each male and female income subgroups are divided into high (solid circle, solid line) and low (hollow circle, dashed line) inequality subgroups. An inequality by AR expression interaction was analyzed for each income group.