慢性应激对执行功能的影响:ERP 研究

In our daily life, we will inevitably meet a variety of stress. The short-term or moderate stress is benefit to an individual’s survival, while long-term stress or chronic stress has adverse effects on people’s physiology and psychology. Stress can lead to an increased activity of the hypothalamic-pituitary-adrenocortical axis (HPA axis). HPA axis releases the glucocorticoids, which can return to the central nervous system to influence the structure and function of the target brain regions, mainly including the prefrontal cortex, amygdale and hippocampus. Hence, stress has impacts on cognition and emotion. For example, stress can impair memory, behavioral decision and leads to emotional disorder. The executive function, which is associated with the prefrontal cortex, is higher-order cognition function, and it has an important significance to an individual’s adaptation and survival, especially in situations of environmental change and stress. Thus it is important to examine the effects of chronic stress on executive functions. The researches which were about the effects of chronic stress on executive function mainly focused on the behavior. Neuroscience study gets less attention. Moreover, the method is unitary; most of stress studies were functional magnetic resonance imaging studies. The event-related potentials technique, known as its high temporal resolution in milliseconds, is an ideal method to more precisely examine alterations in the dynamic time course of neural activity under stress exposure. Therefore, the purpose of the current research was to investigate how chronic stress effects on executive functions by using the event-related potentials technique. We used preparation for a major examination (National Postgraduate Entrance Exam, NPEE) as a chronic stressor. The perceived stress scale and cortisol awakening response were collected to assess the level of chronic stress. We focused on three executive functions, including working memory, response inhibition and error  processing. The main results were as follows: (1) Psychological assessments confirmed that participants in the exam group were indeed exposed to high levels of perceived stress. Endocrinal results revealed a significantly decreased CAR in the exam group compared with the non-exam group, which suggests that exposure to chronic stress leads to reduced adrenocortical activity. (2) Chronic stress may increase the neural activity of the stage of attention allocation in n-back WM task, reflecting on increased P2 amplitude. Furthermore, the group difference in P2 amplitude was most pronounced in participants in the exam group who reported high levels of perceived stress. Correlation analyses showed that the perceived stress score was positively correlated with the P2 amplitude. Instead of better behavioral performance, the exam group used more neural resources to maintain a similar performance with the non-exam group, which may indicate that chronic stress decreases neural efficiency while performing a WM task. (3) Correlation analyses showed that the higher level of stress, the slower the speed of conflict detection in response inhibition, which reflecting on prolonged the latency of NoGo-N2. And this correlation only occurred in the exam group. (4) The exam group showed increased Pe amplitude compared with the non-exam group after committing an error. Participants’ rating of the importance of the exam was positively associated with the amplitude of Pe. These results suggest that chronic stress leads to greater motivational assessment of and higher emotional response to errors. (5) Chronic stress may lead to the decrease of the attention resource after committing an error, which reflected on attenuated P3 amplitude in post-error condition. This research not only facilitates the understanding of the effects of chronic stress on executive functions, but also provides scientific indicators and theoretical basis for stress assessment and intervention.