Abstract: In the context of the effect of acute stress on aggressive behavior, most studies on stress responses involve exposing participants to novel, one-time stressors; however, people are constantly exposed to similar stressors in everyday life multiple times. Compared with the response to one-time exposure to stressors, the ability to adapt to repeated stress has greater evolutionary utility as it preserves resources by relieving the response to non-life-threatening stress; however, little is known about the effect of repeated acute stress on aggressive behavior.
In Study 1, we investigated the effect of repeated acute stress on aggressive behavior. Sixty healthy male college students were selected for this study. A modified version of the Trier Social Stress Test for Groups (TSST-G) was introduced as a standardized, economic, and efficient tool to simultaneously induce a psychobiological stress response in a group of subjects. All participants were exposed to the modified version of the TSST-G twice one week apart. The main characteristic of the stress response is the activation of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic adrenomedullary (SAM) system. The HPA axis responses were assessed by measuring salivary cortisol levels. The assessment of the SAM stress system during the experiment was conducted by monitoring its correlates—heart rate (HR), and emotional responses were assessed by measuring state anxiety. Following the modified version of the TSST-G, the Taylor Aggression Paradigm (TAP) was adopted to induce and measure aggression. Subsequently, according to the social information processing model (SIP), we explored the influence mechanism of repeated acute stress on aggressive behavior. After each of the modified version of the TSST-G, participants completed a dot-probe task and a single-target implicit association test (ST-IAT).
In Study 2, we further investigated the change in aggressive behavior after the regulation of repeated acute stress through internal channels. First, we investigated the change in aggressive behavior after regulating repeated acute stress by changing the frequency of repeated stress. Participants were exposed to the modified version of the TSST-G twice on consecutive afternoons. We then investigated the change in aggressive behavior after the regulation of repeated acute stress by reducing the intensity of repeated stress. The TSST-G control condition contains all factors except for the psychosocially stressful components—socio-evaluative threat and uncontrollability. Participants were exposed to the TSST-G control condition twice, at an interval of one week. Self-reported state anxiety, salivary cortisol levels, and heart rate were assessed during the protocol.
In Study 3, we further investigated the change in aggressive behavior after the regulation of repeated acute stress through external channels. Specifically, using a double-blind, placebo (PL)-controlled between-subjects design, we explored whether intranasal oxytocin (IN-OT) can accelerate the habituation of individuals to repeated stress, thereby reducing aggressive behavior. Participants either took a nasal spray containing oxytocin or a placebo spray. Approximately 40 minutes after OT or PL administration, the participants completed the modified version of the TSST-G. Following the modified version of the TSST-G, the TAP was adopted to induce and measure aggression. Self-reported state anxiety, salivary cortisol levels, and heart rate were assessed during the protocol. The oxytocin receptor (OXTR) genotype is an important factor in IN-OT signal transduction and is also an important reason for individual differences in the behavioral effects of IN-OT. Thus, we further investigated the moderating role of oxytocin receptor genotyping in this process. Specifically, four single nucleotide polymorphisms (SNPs) in OXTR rs53576, rs237887, rs237897, and rs7632287 were tested.
These studies have great scientific and practical significance in providing further empirical evidence to support the phenomenon of HPA habituation and the “fight or flight” theory and reveal the effect of repeated stressors in everyday life on aggressive behavior and cognitive processing mechanisms. Additionally, the study of internal and external regulation will help accelerate an individual's habituation to repeated stress and attenuate the HPA axis responses.

Key words: psychosocial stress, college students, repeated acute stress, aggressive behavior