The Effect Of Sadness On Response Inhibition And Its Neural Mechanism

Response inhibition is one of the most critical ability to control oneself in external environment or inner requirement needed. Serve as one of the classical paradigms to test response inhibition, stop signal task(SST) is a completely suppression of ongoing action. Its strengths are: a stop signal evoke controlling behavior after go signal and these two signals’ interval dynamic changes regularly, and it is capable of quantizing inhibitory behavior although no response occurs when hold up successfully. So the SST is main task to study response inhibition function in the thesis.There are lots of SST theoretical model, in which independent race model is the most widely used. Fronto-basal ganglia circuits, which is the vital neurobiological basis of response inhibition, consist of three neural pathways: direct, hyper-direct, indirect pathways. By means of these three pathways’ function together, only the planning reaction starts and ends as required, others all stop.Emotion is one of important factors effecting on response inhibition. Emotion enable us to identify risks, pursue interests and avoid disadvantages. It is a automatic self protection mechanism forming in long term evolutionary process, and should influence cognitive executive function directly. Its mechanism is not promote or impede cognition functions, instead, various mood states might have independent and crossover dimensions respectively.Sadness is individual experience in unpleasant situation and inner feeling of losing or no gains. Some early researches suggested sadness should reduce the efficiency of attention tasks or constrict attention scales, make individuals tending to self-focus and maintain self-image. Its motivation should be derived from self-protection and avoid unpleasant context. But others showed sadness be related to higher physiological impulsivity, could activate self adaptive response for loss. The tendency to negative scenario such as sadness exists in human beings’ and animals’ information processing including attention, evaluation, response steps extensively, and acts in various kinds of mental operations such as sensory, perception, memory and attention. When individuals are coping with sadness, some cerebral limbic and paralimbic system come into activation.Emotion, response inhibition and gender difference’s interaction mechanism is uncomprehensive and inconsistent in previous studies which may be due to different emotional materials or research paradigms. Furthermore, emotional response inhibition have distinct gender difference. In spite of females are more sensitive in emotional concerned task, it is equally important to study emotion processing mode in males.In this study, for investigating the interaction, neural mechanism and gender difference, college students were major subjects, the traditional SST, the emotion SST were main tasks, the mechanism of sadness acted on response inhibition function was investigated by functional magnetic resonance imaging(fMRI).The first experiment combined traditional SST and emotional SST task which toke the distinguish of emotional valence as the response task, explored the effect of sadness on response inhibition. The first step was choosing valence-matched four groups(male/female, sadness/neutral) consisted of 20 pictures respectively. Recruited 48 southwest university students randomly, executed traditional SST and emotional SST task, in-group independent variables were emotional faces(sadness/neutral), between-group independent variables were gender(male/female), dependent variables were stop signal response reaction(SSRT), stop response reaction time(SRRT), go signal reaction time(GoRT).The results showed that sad SRRT decreased and SSRT increased in emotional SST, especially in females. These results confirmed the negative emotion function hypothesis.The second experiment used emotional SST to investigate the neural mechanism of 32 college students(20 females, 12males) concerning the effect of sadness cognition on response inhibition which is to explore the brain regions’ activated intensity discrepancy in emotional inhibition process and the results suggested that compared neutral emotion, sadness remarkably activated insula, inferior frontal gyrus(IFG), subthalamic nucleus(STN), globus pallidus(GP), thalamus, supplementary motor area(SMA), putamen, middle cingulate cortex(MCC), amygdala, hippocampus and parahippocampal gyrus in inhibitory conditions, compared to females, males’ insula and right IFG activated more in sadness inhibitory task.The third experiment employed psychophysiological interactions(PPI) to study brain regions’ functional connectivity. The 8 representational notably variations brain regions in part A were selected as regions of interest(ROI) including right insula, bilateral anterior cingulate cortex(ACC), bilateral MCC, right amygdala, bilateral parahippocampal gyrus to execute PPI analysis. The results showed that compared neutral condition, sadness leaded to increased activated in(left ACC and parahippocampal), decreased activated in(left ACC and right ACC),(left MCC and right superior frontal gyrus(sFG)/right middle frontal gyrus(m FG)/right MCC),(right amygdala and sFG). And in sadness condition, females showed increased functional connectivity activation in(right ACC and right IFG/middle cingulate cortex/insula/putamen),(left ACC and right SMA),(right MCC and sFG/left ACC),(right insula and right IFG/left MCC/hippocampal/parahippocampal),(left parahippocampal and right IFG/right caudate nucleus/right putamen/right GP/right insula) etc.Sum up above experiments’ consequences, the conclusions in these tests are:(1). the cognition of sadness decreased individuals’ inhibition ability, manifesting as higher SSRT in emotional SST.(2). sadness influenced males and females in different levels, males had no significant results.(3). In inhibition condition, sadness notably activated frontal lobe, basal ganglia and limbic system. Compared with the females, males’ inferior frontal gyrus and insula had increased activation.(4). In inhibition condition, sadness notably activated the functional connectivity between anterior cingulate cortex and parahippocampal gyrus, and had decreased activation between middle cingulate cortex and frontal lobe, amygdala and frontal lobe. Compared with the females, males had decreased activation between anterior cingulate cortex, middle cingulate cortex, insula, parahippocampal gyrus and frontal lobe.