Effects Of Acute Stress And Gender On Cognitive Process

Living in an era of information becoming richer and richer,and more rapidly updating,the human brain has evolved a kind of infor mation-entry mechanisms known as sensory gating,to cope with the massive sensory inputs during the earliest stages of cognitive process.Then,the sensory information can be encoded in a higher stage of cognitive processing,which includes attentional selection and other forms of top-down processing,so that all kinds of cognitive operations in working memory can be carried out smoothly,and the effective output of behavior and adaptation can be achieved finally.However,the stresses in life always come unexpectedly,and how they will affect the individual’s cognition has received little attention in previous studies.Especially from the pathological hypotheses of mental disorders,the important roles of stress events or its cumulative effect can always be seen（such as the popular Vulnerability-stress Model）,So this is an urgent subject that needs to be explored thoroughly.According to the relevant documents,sensory gating abnormalities are widely considered to be biological markers of schizophrenia spectrum disorders,and inhibitory dysfunction is the direct cause of various substance abuse disorders,impulsivity disorders and other abnormal control of behaviors.Although working memory is a resource-limited system for short-term storage and processing of information,it is closely related to attention control,emotion regulation and overall rational cognition,and is the basis of human complex behaviors.Therefore,understanding of the pathological mechanisms of many kinds of mental disorders can always be achieved directly or indirectly from the perspective of abnormal working memory funtions.However,it is still unclear how these three cognitive functions are affected by acute stress.Additionally studies have shown that there are significant differe nces between genders in the typical incidence,course and prognosis of broad mental disorders.However,uptill now,only a few studies have investigated the effects of acute stress on cognitive processing,much fewer of which focused on gender differences.The neural mechanism of the effects of acute stress on cognition and gender differences are still poorly understood.The present work attempts to tap the cognitive mechanism and its gender difference behind the behavorial performance under stressful situations.Therefore,working memory was investigated firstly.Then on the basis of the findings,more efforts was made to try to clarify the mechanisms behind the cognitive process in WM task.O ne by one,we concerned the effects of acute stress and gender on sensory gating,and inhibition function.Thus this thesis includes four related but relatively independent studies as follows.The first study concerned the effect of acute exposure to the stress and gender difference in working memory by using n-back task.N inety eight middle school students（47 men）participated in the present study.All subjects were exposed to either the social pressure stress or the control treatment after they were randomly divided into the stress group or the control group,and then engaged in the experimental task.The results revealed a successful induction of activation by stress intervention,which increased the reaction times for right responses and decreased the accuracies but only data of women reached significant level.Altho ugh the results showed the stress disrupted WM functions more severely in women than men and presented relatively uniform findings from others,they were insufficient to clarify the gender differences in cognitive process and it was necessary to perform further analyses at the level of neural process。The second study investigated the effect of gender and acute exposure to the stress on working memory in university students by using an adapted Vogel et al.’s lateralized change detection task.In this paradigm,a lateral ERP wave elicited by the memory array was recorded,from which three components that indexed respectively attentional selection of the stimuli（the N₂pc）,object identification and classification（the early contralateral delay activity,the early CDA）and the maintenance of WM representations（the late contralateral delay activity,the late CDA）were extracted precisely.This experiment was conducted by adopting a within-subject design,in which CPS and control procedures were respectively applied on forty-five volunteers（21 men）in the same time period of the experiment days by an interval of at least 24h,and treatment order was counter-balanced.Then all subjects were engaged in the WM task.This study was among the first ones to investigate the effects of acute stress and gender on human WM process by using time-domain anlysis of the ERPs.The results showed a successful induction of a neuroendocrine stress response,which had substantial and detrimental effects on WM performance and women were more severely damaged than men.As for the process of WM,the detrimental effects emerged at least as early as N₂pc time window,as well as the gender difference,and the interactions between treatments and genders persisted throughout the whole WM process.Therefore,the findings of the present study extend ed the recent literature investigating the effects of acute stress on human WM processing.Given that the detrimental effects emerged at least as early as N₂pc time window in Study 2,the third study concerned sensory gating measured by paired-click paradigm in order to make sure how the effects of stress and gender are going on at the earlier stage of information processing.This experiment was conducted by adopting a within-subject design,in which CPS and control procedures were respectively applied on forty one university students（24 men）in the same time period of the experiment days by an interval of at least24h.All subjects were then engaged in the paired-click task shortly after the stress and control treatment.The results showed a successful induction of a neuroendocrine stress response,and the stress response disrupted P₅₀sensory gating via impairments of the inhibition of redundant information without effects on sensory registration.There is no gender difference in the adverse effects of stress on P₅₀sensory gating.Additionally the current study also indicated that CPS disrupted allocation of attention resources,reflected by atte nuated activation during P₂₀₀time window for both genders after CPS relative to after control procedures.Based on the discussions of the second study,the adverse effects of acute stress on working memory are most likely related to impaired inhibitory function,which inspired the following study.The fifth study focused on the effects of acute exposure to the stress on inhibitory function and gender difference in university subjects by using a color-word Stroop task,and the activation of the subjects’frontal lobes during performing the task was monitored by functional nearinfrared spectroscopy（f NIRS）.This study was conducted by adopting a repeated-measurement design,in which forty-seven university students（24 men）were engaged in the Stroop task befo re and after the CPS intervention during the same experimental session.The findings indicated a successful trigger of a neuroendocrine stress response,and CPS had substantial effects on Stroop task performance with gender difference that women showed an overall decrease in RTs of all three types of trials compared with that of men,which was also evidenced by changes of oxygenated hemoglobin in the left and right dl PFC.Based on the comprehensive analysis of the findings of this study and the data from study I and Study II,it was concluded that women were more severely disrupted than men in inhibition function after exposure to stress,and the findings of the present study supported the hypothesis that acute stress leads to shifts in neural functioning network.Additionally it was addressed about the measurements of inhibiton in the final discussion of this serial studies.It was generally discussed on the results of the four studies based on four aspects respectively:the mechanism of stress effects,the inhibition function and its measurement,the effect of acute stress on cognitive process and gender differences,and the practical applications.In this part it was further clarified about the concepts of gating function and inhibitory control,the relatio nship between working memory and inhibition function as two core components of executive control,the relations and differences between stress and physiological arousal,and the shifts from flexible,goal-directed and prefrontal cortex-dependent behavior,to more rigid stimulus-response behavior as well.Meanwhile it was discussed about the difficulties in measurement of inhibition and the possible solutions.The findings of the serial studies generally supported and extended the assumption that acute stress led to large-scale neural network shifting underlying cognition and responses to gain better living.Finally,a preliminary discussion was made on the applications of these findings in real practices.The following conclusions were drawn from the present thesis.Firstly,acute stress substantially disrupted subjects’sensory gating functions without gender difference.Secondly,acute stress significantly damaged the individual’s working memory performance with gender effect.In terms of cognitive process,acute stress impaired the distribution of attentional resources and working memory inhibition of task-irrelevant information.As a result,plenty of redundant and irrelevant information was represented and stored in WM,and gender difference in the stress-related detrimental effects emerged at least as early as N₂pc time window.Thirdly,acute stress strongly affected the individual’s normal stroop interference and stroop facilitation with clear gender differences.And the neural network in dl PFC areas involved in the effect of gender and acute exposure to stress on inhibitory function.