Endocrine Stress Response

Salivary cortisol, a reliable measure of HPA axis reactivity, was collected using Salivette swabs (Sarstedt^®, Nümbrecht-Rommelsdorf, Germany). Measurements occurred at five time points throughout the experiment: −60, −20, +12, +50, +60 min, relative to stress or control treatment onset. Samples were kept on ice during the session, centrifuged at 3,000 rpm at 4°C for 10 min directly following the experimental task, and stored at −70°C. Cortisol concentrations were analyzed via a commercially available ELISA kit (Salimetrics), following the manufacturer’s instructions. Inter-assay coefficient of variation ranged from 6.1 (high control) to 7.5% (low control), and intra-assay coefficient of variation was 5.3%. Changes in cortisol levels were calculated using Area Under the Curve with respect to increase (AUCi), following the procedures described by Pruessner et al. (2003). Note that the Pruessner et al. (2003) paper describes two methods for assessing cortisol reactivity, AUCi and AUCg (Area Under the Curve with respect to ground). We elected to use AUCi rather than AUCg because we were interested in capturing sensitivity to stress, rather than total cortisol output. However, we note that our findings are not dependent on this decision and our robust to either measure.