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.

(HT: Brendan Coates)

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6 Responses to Stressed Out on Struggle Street

  1. Michael W says:

    Isn’t there still the possibility that the direction of causation between allostatic load and memory could be the opposite of that claimed?

    Couldn’t a poor working memory lead a person to be poorer at assimilating and adjusting to putative ‘stressful’ events, so that the limited memory capacity prevents a person from ‘processing’ the stressful event so as to put it ‘out of their mind’?

  2. Thinking in old ways says:

    Andrew

    As with Michael W I think the question of direction of causation is very important here, as is the need to be clear about what we are talking about in terms of “intergenerational cycles of poverty”. That is whether it is the “poverty” which is relevant, or whether it is the parental characteristics that count (or possibly just relative socio-economic status – regardless of actual levels of deprivation).

    There is an interesting new paper out by some of your colleagues (Taking Chances: The Effect of Growing Up on Welfare on the Risky Behavior of Young People, by Deborah Cobb-Clark, Chris Ryan, Anastasia Sartbayeva) available for download at http://ftp.iza.org/dp4095.pdf which suggests that it is the parental characteristics that appear to count – not the level of welfare dependency (often used synonymously as a measure of ‘poverty’).

    There is also a useful survey by the OECD of intergenerational disadvantage at
    http://www.oecd.org/dataoecd/27/28/38335410.pdf

    I guess I am also a little bit concerned about the stress approach from two other perspectives:

    1. This line of argument has been used in discussions about child care where studies have been undertaken looking at levels of stress hormones in children in child care and being cared for at home. And while I might be wrong I don’t think the evidence on child care outcomes necessarily matches up with the evidence on stress levels in children in childcare settings;

    2. Of course what one is talking about is relative well-being rather than absolute poverty – and this goes back to the question of inequality and health outcomes – and my recollection is that when the BMJ looked compreshensively at this they found there is little evidence of inequality per se being linked with poor health outcomes – although there is a very strong health gradient – and the role of stress in this of course is something that has been debated since the original Whitehall study.

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  4. Andrew – I haven’t followed the positive pyschology literature closely, but I think one of their claims is to be able to teach better methods of handling stress. Indeed, I thought after the Layard book that this was going to be the latest wave of social democratic nanny state activity, with a massive increase in the number of psychologists.

  5. gordon says:

    I’m not sure how this works – I commented on this post where it appeared on “Core Economics”. Are there two parallel blogs?

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