What is socioeconomic status (SES), and why would a cognitive neuroscientist be interested in it?
Volumes have been written about the first question, but for present purposes I will simply say that virtually all societies have better off and less well off citizens. Differences in material wealth tend to be accompanied by noneconomic differences in educational opportunity and attainment, social prestige and control over one’s life circumstances.
The relevance of SES to cognitive neuroscience lies in its surprisingly strong relationship to cognitive ability, as measured by IQ and school achievement, beginning in early childhood. Which neurocognitive systems underlie these SES gradients in psychological functioning, and what causes the gradients? These are questions for cognitive neuroscience.
The neurocognitive profile of childhood SES. Early work from my lab sought to characterize SES disparities in terms of cognitive neuroscience’s model of the mind, rather than in terms of intelligence or achievement test scores. That is, we used neuroscience’s parse of the developing mind to derive a neurocognitive “profile” of the systems that are relatively more and less strongly associated with SES. Three initial studies, undertaken with Kim Noble, Hallam Hurt, Laura Betancourt and others, showed a fairly consistent profile of neurocognitive ability associated with SES in children of different ages (Noble, Norman & Farah, 2005; Farah, et al., 2006; Noble et al., 2007).
Among the most pronounced disparities were executive function (EF), associated with prefrontal cortex, and declarative memory, associated with the hippocampus. In subsequent studies with Gwen Lawson and others, we found evidence for anatomical differences in prefrontal cortex, consistent with findings of EF disparity and also determined that SES disparities in EF contribute to the SES academic achievement gap (Lawson, et al., 2013; Lawson & Farah, 2015).
How does SES affect brain development? Describing the relations between SES and brain development is only of interest insofar as it gives us clues to the mechanisms by which SES shapes child development. Childhood poverty is associated with high levels of stress and low levels of cognitive stimulation, and these are among the likely causes of SES disparities.
Animal research has shown that stress affects the development of the PFC (already mentioned in relation to EF) and hippocampus (crucial for memory, as well as for stress regulation), and that maternal nurturing behavior buffers the hippocampus from stress (Hackman et al., 2010). We found that early childhood parental nurturance predicts hippocampal volume in adolescence (Rao et al., 2010) and also predicts stress responsivity (Hackman et al., 2013), supporting the relevance of this mechanism to human development. Cognitive stimulation has partly distinct effects from parental nurturance on cognitive and brain development (Avants et al., 2015; Farah et al., 2008).
Next steps. We have only begun to study the complex system of biological and social factors responsible for SES disparities. Luckily, researchers from many different institutions are now involved in the effort. Current work at Penn, with Laura Betancourt, Daniel Hackman, Hallam Hurt, Gwen Lawson and others, is examining the developmental origins of SES neurocognitive disparities (eg, Betancourt et al., 2015), their longitudinal stability (eg, Hackman et al., 2014, 2015), and their status in young adulthood (Lawson et al., in prep).
Why is this important?
People of low SES face enormous economic and social barriers to improving their lives. It is a tragic irony that they so often face this challenge with diminished capabilities as a result of the hardships experienced early in life. The ultimate goal of this research program is to understand and help break the cycle of poverty using insights from neuroscience.