The impact of stress on the prefrontal cortex: a view of how socioeconomic status impacts executive function
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By the time they reach kindergarten, children from low Socioeconomic (SES) backgrounds lag behind their high SES peers in a host of cognitive abilities including executive function. The mechanism of how SES impacts executive function is still unclear; however, recent research eludes to the effects of stress regulation of the Hypothalamus-Pituitary-Adrenal (HPA) axis on cortical development as a promising explanation. Children raised in low SES backgrounds are exposed to a multitude of environmental stressors that can impact the child’s development of their stress response and regulation within the HPA axis. Alterations within the HPA axis, particularly cortisol levels, are shown to impact brain development especially the prefrontal cortex (PFC) which is a major region supporting executive function. Although the stress regulation mechanism seems valid, the influence of early life stress on the PFC and subsequent executive function outcomes have not been directly tested. The current study aimed to examine how earlier and concurrent responses to stress, as reflected in measures of cortisol reactivity, relate to neural and behavioral measures of executive function within the framework of how SES impacts executive function. This longitudinal study consisted of two waves of data collection, the first wave was collected when the children were 3-5 years old and the second wave when the children were 7-10 years old. Measures of executive functioning and cortisol stress response were collected during both waves, whereas structural and functional magnetic resonance imaging (MRI) of the brain were collected at the second wave. Although multiple analyses were conducted and numerous nonsignificant results were present, the significant results suggest variations in cortisol reactivity relate to executive function, overall brain volume, and regional differences in cortical thickness within the PFC including middle frontal cortex, inferior frontal cortex, insula, and anterior cingulate cortex. Within the bigger SES framework, SES was related to cortisol reactivity and executive function. SES differences were found in total grey matter and regional cortical thickness within the PFC including the insula and anterior cingulate cortex. The cortical thickness of the right inferior frontal cortex mediated the association between SES and executive function. The inferior frontal cortex and the anterior cingulate cortex were associated with both cortisol reactivity and SES suggesting these regions may contribute to the mechanism of how SES impacts executive function via stress regulation or dysregulation. Although future studies are necessary to replicate findings on a larger scale, the current study is an encouraging step towards understanding how differential stress responses along the socio-economic ladder impact brain and cognitive development.