Prefrontal cortical thickness mediates the association between cortisol reactivity and executive function in childhood.

The impact of stress hormones, such as cortisol, on the brain is proposed to contribute to differences in executive function of school-age children from impoverished backgrounds. However, the association between cortisol reactivity, prefrontal cortex, and executive function is relatively unexplored in young children. The current longitudinal study examined whether 63 children's early preschool-age (3-5 years, Time 1) and concurrent school-age (5-9 years, Time 2) salivary cortisol reactivity were associated with executive function and prefrontal cortical thickness at school-age. Two measures of cortisol reactivity were calculated: area under the curve with respect to ground (AUCg; total cortisol release) and with respect to increase (AUCi; total change in cortisol). Results demonstrated that Time 2 total cortisol release was negatively associated with executive function, Time 1 total cortisol release positively related to right middle frontal cortical thickness, and Time 2 total cortisol change was negatively associated with right inferior frontal cortical thickness. Moreover, greater right middle frontal cortical thickness mediated the association between greater Time 1 total cortisol release and lower executive function. This study provides support for an early adversity framework in which individual differences in executive function in childhood are directly related to the variations of cortisol-release and the effects on the prefrontal cortex thickness.