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374 REVERSIBLE DISORDERS OF BRAIN DEVELOPMENTis a function of the brain. Yet little is currently known about the relationship betweenSES and brain function, in terms of two key issues: the specific brain systemsthat correlate with SES and the mechanisms by which these correlationsemerge. The goal of this chapter is to review some preliminary studies that addressthese issues.We begin with the first issue: the characterization of the SES gap in children’sneurocognitive development in terms that can be related to current cognitive neuroscienceconceptions of mind and brain. One hypothesis is that SES correlates withall neurocognitive systems equally, across the board. Alternative hypotheses are thatSES correlates with certain systems more than others. There is already reason tobelieve that the development of the brain systems underlying language system isassociated with SES, as a number of relatively pure tests of language developmenthave revealed a robust SES gap (Whitehurst, 1997). Would other systems that, likelanguage, undergo prolonged postnatal development also show specific sensitivityto SES? Prefrontal cortex is a brain region that continues to mature throughout childhood,with pronounced cellular changes in the preschool and early childhood years(Johnson, 1997). It is also a region on which many of the cognitive achievements ofearly childhood depend (Case, 1992; Diamond, 1990; Diamond, Prevor, et al., 1997;Johnson, 1997; Posner & Rothbart, 1998). A disproportionate effect of SES on prefrontalfunction is therefore a hypothesis of particular interest.Neurocognitive Correlates of SESThe first set of studies reviewed here was aimed at characterizing the neurocognitiveprofile of poverty. They take, as their starting point, the existence of anSES gap in cognitive achievement and ask, Is the SES gap uniform over differentneurocognitive systems, or is the development of some systems more stronglycorrelated with SES than others? We have so far addressed this question in threedifferent studies. The three are distinguished primarily by the ages of the childrenwho participated and the specific neurocognitive tasks used to assess the children’sbrain development. In addition, two of the studies compared groups of low andmiddle SES children, whereas one analyzed children’s task performance as a functionof continuously varying SES.In an initial study we compared the neurocognitive performance of 30 low and30 middle SES African American Philadelphia public school kindergarteners(Noble, Norman, & Farah, 2005). SES was established on the basis of parentaleducation, job status, and family income-to-needs ratio. The children were testedon a battery of tasks adapted from the cognitive neuroscience literature, designedto assess the functioning of five key neurocognitive systems. These systems aredefined in anatomical and functional terms—that is, based on their brain localizationsand the kinds of information processing for which they are used.