Poverty and brain development
Chapter 8 endnote 1, from Lisa Feldman Barrett.
Some context is:
...if a culture dictates that people with certain skin colors are less worthwhile, this social reality has a physical effect on the group: they have lower salaries and their children have poorer nutrition and living conditions. These factors change the structure of their children’s brains for the worse, making school harder and increasing the odds that the children will earn lower salaries in the future. [...] The human brain develops until late adolescence, but the most sensitive time begins during the first trimester and continues throughout the first several years of life, particularly for brain regions important for body-budgeting, control, and learning (Hill et al. 2010). These brain regions are thinner (fewer connections between neurons, or even fewer neurons) in infants and young children raised in poverty. Importantly, their brains do not start off smaller but grow more slowly over the first three years of life (Hanson et al. 2013); the growth occurs particularly in the connections between neurons (Kostović and Judaš 2015), so reduced connectivity will limit conceptual development and speed of processing, which is strongly related to IQ. Social reality thus becomes physical reality....
Chapter 13 endnote 18, from Lisa Feldman Barrett.
Some context is:
Poorer nutrition equals a thinner PFC, which is linked to poorer performance in school, and less education, like not completing high school, leads back to poverty.
All mammalian brains have more or less the same parts. If you look at the brains of many different kinds of mammals, you can see that the structural elements are conserved. Also, brains develop on a fixed schedule — the order of events (when neurons are born, when axons grow, when synapses develop, etc.) is the same whether we are talking about a mouse or a human. What does change is the duration of each developmental period. A longer developmental window for, say, axon growth, means there is more opportunity for the environment to influence that feature of the brain. Scientists call this the translating time model of brain development. The upshot is that the same plan for brain design can produce very different brains across species. It also helps explain some individual differences in brain structure and function across people.
We humans are born a little earlier than our closest animal cousins and are weaned much earlier. Much of your brain development was finished outside the uterus of your mother, and the long window of brain development in infancy and childhood (into adolescence) allowed your brain to wire itself to its physical and social circumstances.
The same is true for people who were born into and live in poverty. They were likely exposed to poor nutrition, overcrowding, noise, temperature fluctuations, and various forms of interpersonal stress that influenced their brain development. These factors negatively influence brain development. Brains that are bathed in poverty develop with smaller structures and less surface area. These differences are linked to poorer school performance.
The translating time model leads us to expect that early poverty will be a better predictor of later school performance and IQ than poverty later in childhood, and this is, in fact, the case (a finding that cannot be explained by genes). Interestingly, in poverty, environmental influences impact IQ most, whereas in wealthier families, genes account for almost all the variance (because all environmental factors are good).
It is even possible that a mother's chronic stress (i.e., running a chronic deficit for her body's budget) can affect the brain development of her unborn fetus. It has been demonstrated that prenatal stress influences the structure and function of the peripheral nervous system (via the hormone cortisol that can cross the placenta).  In adolescents and adults, chronic body misbudgeting and increased cortisol is associated with neuron death in several key brain regions known to be important for school performance (e.g., the prefrontal cortex and hippocampus). It's not that far a leap to suggest the hypothesis that a mother's stress can sculpt her fetus's brain. This hypothesis is still speculative, but there is evidence consistent with it.
The bottom line, as I write in chapter 13, is that society's stereotypes about poverty and race, which are social reality, can become the physical reality of brain wiring, thereby making it seem as if the cause of poverty were simply genes all along.
For a friendly blog post on this topic, see "Poverty on the Brain."
Notes on the Notes
- Puelles, Luis, Megan Harrison, George Paxinos, and Charles Watson. 2013. "A developmental ontology for the mammalian brain based on the prosomeric model." Trends in Neurosciences 36 (10): 570-578.
- Workman, Alan D., Christine J. Charvet, Barbara Clancy, Richard B. Darlington, and Barbara L. Finlay. 2013. "Modeling transformations of neurodevelopmental sequences across mammalian species." The Journal of Neuroscience 33 (17): 7368-7383.
- To read accessible magazine articles on the topic, see "How Poverty Affects the Brain" (Newsweek) and "What Poverty Does to the Young Brain" (New Yorker).
- Luby, Joan L. 2015. "Poverty’s most insidious damage: the developing brain." JAMA Pediatrics 169 (9): 810-811.
- Hanson, Jamie L., Nicole Hair, Dinggang G. Shen, Feng Shi, John H. Gilmore, Barbara L. Wolfe, and Seth D. Pollak. 2013. “Family Poverty Affects the Rate of Human Infant Brain Growth.” PLOS One 8 (12): e80954. doi:10.1371/journal.pone.0080954.
- Hair, Nicole L., Jamie L. Hanson, Barbara L. Wolfe, and Seth D. Pollak. 2015. "Association of child poverty, brain development, and academic achievement." JAMA Pediatrics 169 (9): 822-829.
- Noble, Kimberly G., Suzanne M. Houston, Natalie H. Brito, Hauke Bartsch, Eric Kan, Joshua M. Kuperman, Natacha Akshoomoff, David G. Amaral, Cinnamon S. Bloss, and Ondrej Libiger. 2015. “Family Income, Parental Education and Brain Structure in Children and Adolescents.” Nature Neuroscience 18 (5): 773–778.
- Duncan, Greg J., W. Jean Yeung, Jeanne Brooks-Gunn, and Judith R. Smith. 1998. "How much does childhood poverty affect the life chances of children?." American Sociological Review 63 (3): 406-423.
- Turkheimer, Eric, Andreana Haley, Mary Waldron, Brian D'Onofrio, and Irving I. Gottesman. 2003. "Socioeconomic status modifies heritability of IQ in young children." Psychological Science 14 (6): 623-628.
- Glover, Vivette, T. G. O’connor, and Kieran O’Donnell. 2010. "Prenatal stress and the programming of the HPA axis." Neuroscience & Biobehavioral Reviews 35 (1): 17-22.
- Also see "Stress and Pregnancy (Prenatal and Perinatal)" (child-encyclopedia.com).
- Bruce McEwen papers [full reference to be provided]
- Lou, Hans C., Dorthe Hansen, Merete Nordentoft, Ole Pryds, Flemming Jensen, Jette Nim, and Ralf Hetnmingsen. 1994. "Prenatal stressors of human life affect fetal brain development." Developmental Medicine & Child Neurology 36 (9): 826-832.
- Coe, Christopher L., Marian Kramer, Boldizsár Czéh, Elizabeth Gould, Alison J. Reeves, Clemens Kirschbaum, and Eberhard Fuchs. 2003. "Prenatal stress diminishes neurogenesis in the dentate gyrus of juvenile rhesus monkeys." Biological Psychiatry 54 (10): 1025-1034.
- Koning, Irene V., Myrte J. Tielemans, Freek E. Hoebeek, Ginette M. Ecury–Goossen, Irwin KM Reiss, Regine PM Steegers-Theunissen, and Jeroen Dudink. 2016. "Impacts on prenatal development of the human cerebellum: A systematic review." The Journal of Maternal-Fetal & Neonatal Medicine. http://dx.doi.org/10.1080/14767058.2016.1253060