Time Course Of Psychological Stress

The state that the organism homeostasis being threatened called stress.To far, researches about psychological stress mainly focus on two aspects:first, behavioral researches on neuroendocrine response and its mediators induced by psychosocial stress; second, brain imaging researches on the neural mechanisms of psychological stress, aimed to determine the the brain spatial orientation during psychological stress. Most researches which adopted event-related potentials(ERP) technique measured subjects’normal stress level by scales, or make subjects in physical stress by raising the level of cortisol, then focus on the effect of stress on other cognitive tasks, so the brain neural activity of psychological stress itself was ignored. All three typical research paradigm of psychological stress are not apply to ERP technique because of laboratory changing, oral report and complex interface.Therefore, the present study attempts to explore a new psychological stress paradigm, estimation task, to fill the gap, then to reveal the time course of neural activity during psychological stress, so that the time and space parameters can be provided for psychological stress by combine with brain imaging technology. Mental arithmetic task under time pressure is used to induce subjects’responses of stress, meanwhile the complex interface, laboratory changing and oral report which can increase EEG noise were overcome.Study1aimed to make a behavioral validity test of responses of psychological stress induced by estimation task, by collecting subjective stress indicators(subjective stress and subjective anxiety) and objective stress indicators(saliva cortisol). In order to avoid the experiment being disturbed by the metabolic rhythm of saliva cortisol,14college students were selected to complete the estimation task in14:00pm in each day. The task consists of5stages:baseline1(staring at the figures presented randomly), control condition(complete easy mental arithmetic task without social-evaluative threat), stress condition(complete difficult mental arithmetic task under social-evaluative threat), baseline2(staring at the figures presented randomly), and rest(no task),10minutes each stage. Results showed that the stress level and anxiety level after stress condition was significantly higher than control condition and baseline, suggesting that the estimation task can induce subjects’responses of stress in subjective indicators effectively. The saliva cortisol showed obviously increasing from the10minutes after stress condition, and continue rising untile20minutes, suggesting that the estimation task can also induce subjects’responses of stress in objective indicators effectively.Study2aimed to explore the time course of the neural activity during psychological stress,so the estimation task was applied to ERP technique which has high temporal resolution, and arithmetic difficulty was added to the independent variables in order to make a distinction between time pressure and arithmetic difficulty.31college students were selected to join a2-by-2two-factor mixed experimental design, groups(time pressure/no time pressure) by arithmetic difficulty(difficult/easy), in which the groups is between subjects and the arithmetic difficulty is within subjects. Results found that the reaction time was shorter under time pressure or to easy arithmetic on the behavior data. EEG data showed that easy arithmetic under time pressure can induce significantly larger N1amplitude, longer P2latency and larger P300amplitude than easy arithmetic without time pressure; difficult arithmetic under time pressure can also induce significantly larger Nl amplitude, longer P2latency and larger P300amplitude than difficult arithmetic without time pressure, but the main effect of group can only be found on part of the electrode point.In conclusion, estimation task successfully induced responses of stress in both subjective indicators and objective indicators. Compared to Trier Social Stress Test(TSST), the fixed experiment location of estimation task avoid the trouble that changing experimental room based on different experimental tasks; compared to the Montreal Imaging Stress Test(MIST), the simple and pure interface in estimation task can solve the problem that the neural activity induced by target stimulus cannot be separated as synchronized presentation of many stimulus; compared to mental arithmetic task, submit answers through keyboard instead of oral report in estimation task can reduce the artifactual EEG result from head movements when the oral report happens. These advantages let the estimation task be considered as the new paradigm of psychological stress for ERP technology. The EEG component induced by the estimation task is stable, whether to easy or difficult arithmetic, the psychological stress experience can be induced as long as the time pressure existing. A brief "blanking period" happened in the brain at the begin of psychological stress, then the perceptual analysis of stimulus and the capture of attention resource become more difficult in the early stages of the cognitive processing, the same stimulus become relatively larger perceptual load, the time required for allocation of attention is longer, the processing of stimulus become less efficiency, more cognitive resources were occupied during later post-perceptual processes.