I’ve already noted the correlation between a low IQ and poverty, but now The Economist has a summary of how poverty and stress affects the brain.
The reduced capacity of the memories of the poor is almost certainly the result of stress affecting the way that childish brains develop. […]
To measure the amount of stress an individual had suffered over the course of his life, […] researchers used an index known as allostatic load. This is a combination of the values of six variables: diastolic and systolic blood pressure; the concentrations of three stress-related hormones; and the body-mass index, a measure of obesity. For all six, a higher value indicates a more stressful life; and for all six, the values were higher, on average, in poor children than in those who were middle class. […]
The capacity of a 17-year-old’s working memory was also correlated with allostatic load. Those who had spent their whole lives in poverty could hold an average of 8.5 items in their memory at any time. Those brought up in a middle-class family could manage 9.4, and those whose economic and social experiences had been mixed were in the middle.