Abstract
Freezing is a major defensive stress-response, characterized by reduced body-sway and heart rate. Exacerbated freezing in threatening situations has been associated with increased basal and stress-induced glucocorticoid levels and with long-lasting stress-related symptoms in animals. However, the effects of stress-induced changes on human freezing are unknown. A new measure has been developed to quantify freezing-like behavior in humans using a stabilometric force-platform such that shifts in body-sway can be assessed with high temporal and spatial accuracy. Previous research has shown that exposure to angry (vs. neutral) faces can induce reductions in body-sway and heart rate in humans. In our study, we used this method to assess the effects of stress and stress-induced cortisol on human freezing responses to angry versus happy and neutral faces. Participants were 90 adolescents (age 17) who were tested at three time points: prior to, immediately after, and 55 min after the Maastricht Acute Stress Test. To ascertain stress-induction, self-reported, physiological, and hormonal measures were collected prior to, immediately after, and 20, 30, 40, and 55 min after stress-onset. Preliminary analyses of the self-report and blood pressure measures indicated a successful stress-induction. Additionally, we predicted that stress-induced cortisol levels are associated with increased freezing. Finally, we will explore the association between stress-induced freezing and affective symptoms (e.g., anxiety) to gain a better understanding why adolescence is a phase of increased vulnerability for stress-related symptoms. We will discuss our results in terms of the translation between animal and human models of stress and defensive responses to threat.
