Stressed Out on Struggle Street

From this week’s Economist, some evidence that stress might help explain intergenerational cycles of poverty.

The crucial breakthrough was made three years ago, when Martha Farah of the University of Pennsylvania showed that the working memories of children who have been raised in poverty have smaller capacities than those of middle-class children. Working memory is the ability to hold bits of information in the brain for current use—the digits of a phone number, for example. It is crucial for comprehending languages, for reading and for solving problems. Entry into the working memory is also a prerequisite for something to be learnt permanently as part of declarative memory—the stuff a person knows explicitly, like the dates of famous battles, rather than what he knows implicitly, like how to ride a bicycle.

Since Dr Farah’s discovery, Gary Evans and Michelle Schamberg of Cornell University have studied the phenomenon in more detail. As they report in this week’s Proceedings of the National Academy of Sciences, they have found that 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, the two 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.

These two correlations do not by themselves prove that chronic stress damages the memory, but Dr Evans and Dr Schamberg then applied a statistical technique called hierarchical regression to the results. They were able to use this to remove the effect of allostatic load on the relationship between poverty and memory discovered originally by Dr Farah. When they did so, that relationship disappeared. In other words, the diminution of memory in the poorer members of their study was entirely explained by stress, rather than by any more general aspect of poverty. …

That stress, and stress alone, is responsible for damaging the working memories of poor children thus looks like a strong hypothesis. It is also backed up by work done on both people and laboratory animals, which shows that stress changes the activity of neurotransmitters, the chemicals that carry signals from one nerve cell to another in the brain. Stress also suppresses the generation of new nerve cells in the brain, and causes the “remodelling” of existing ones. Most significantly of all, it shrinks the volume of the prefrontal cortex and the hippocampus. These are the parts of the brain most closely associated with working memory.

Children with stressed lives, then, find it harder to learn. Put pejoratively, they are stupider. It is not surprising that they do less well at school, end up poor as adults and often visit the same circumstances on their own children.

I’ve also seen some unpublished work by Christopher Jencks suggesting that the large life expectancy gap between the rich and the poor might be best explained by stress. I’ll post it if I can.

The difficult thing for public policy is that the tools in our armoury aren’t very good at reducing stress. We know a lot about raising incomes, a bit about improving test scores, and something about moving people into employment; but stress isn’t an outcome we’re very good at affecting.

4 thoughts on “Stressed Out on Struggle Street”

  1. So the difference in average number of items held in memory is no more than o.9 items? Yep, that’d do it everytime! 🙂 Doesn’t quite explain how grinding poverty and abusive family life can throw up some damn fine minds if one looks back through history.

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  2. The response will no doubt be a revival of “stress management techniques”, aka “how to have causes without effects”.

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  3. Aha! Found it! I knew this was something I’d read about years ago.  Starting in the 1960s Sir M. Marmot (Prof. of Epidemiology & Pub. Health, University Coll. ,  London) did very big studies on Brit. civil servants (the Whitehall Studies), finding poorer health and higher levels of stress in the lower ranks. He explained a large part of the poorer health outcomes in terms of higher stress, and explained the higher stress in terms of lower level of job control.

    From an interview: “…we showed very clear social differences in people’s experience of the workplace — how much control they had at work, how fairly they were treated at work, how interesting their work was. We found clear social gradients in people’s participation in social networks. We found social gradients in psychological attributes like hostility. …   So then the question is, what is it about position in the hierarchy that determines different rates of disease? …But, more importantly, it suggests what is it about where you are in the hierarchy that’s related to disease, and can we do something about that? So you ask, is it money? Is it prestige, self-esteem? And, in fact, what I think is, it is has much more to do with how much control you have over life circumstances, and the degree to which you’re able to participate fully in society; what Amartya Sen calls capabilities”.

    So there you are. Not so much a stress-health link as a stress-health-worklife link. Hierarchies are bad for youunless you’re at the top.

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  4. And just to thoroughly overreact, there is a link to the ABC Radio  “Health Report” series called “Mastering the Control Factor” (broadcast end 1998/early 1999) here. Norman Swan interviewed several people, incl. Prof. Marmot.

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