The Study Of The Mechanism Of Conflict Effect Based On FMRI And TDCS

In our daily life,the ability of selectively processing the information in changeable environment is necessary for us and this process needs the involvement of cognitive control.In laboratory researches,there are many experimental paradigms to study cognitive control,such as the Flanker task,the Stroop task and the Simon task.Subjects have to neglect the interference of the distractors and make correct response as soon as possible.Here,there are congruent trials(the distractor is same as the target)and incongruent trials(the distractor is different from the target)in these tasks.Previous studies have indicated that the reaction time in the incongruent trials are significantly higher than those in the congruent trials and this phenomenon was named as conflict effect.Recent studies have shown that the strength of the functional connectivity associates with the cognitive behaviour performance.Whether the functional connectivity can be used to predict the conflict effect is still not clear.Thus the first purpose of this thesis was to explore whether the functional connectivity between conflict-related brain regions could predict the behaviour results using the functional magnetic resonance imaging(f MRI)in the Flanker task.The behaviour results showed that the performance of reaction time and the accuracy in the congruent trials was better than that in the incongruent trials.The imaging results showed that in the high-conflict incongruent trials,the activity in the bilateral prefrontal cortex,right superior frontal cortex,bilateral supplementary motor area,bilateral postcentral cortex,bilateral superior parietal lobe and bilateral inferior parietal lobe were significantly higher than the ones in the low-conflict congruent trials showing that these regions were involved in the conflict processing.The regression analysis results of the functional connectivity and the behaviour performance indicated that the strength of the functional connectivity between the left inferior parietal lobe and right supplementary motor area negatively associated with the conflict effect and contributed most to it and the stronger the functional connectivity,the smaller the conflict effect.In contrast,the functional connectivity between the left precentral cortex and right superior frontal cortex,the functional connectivity between the right superior parietal lobe and right inferior parietal lobe were both positively related to the conflict effect meaning that they both did harm to the conflict effect.Finally,the predicted value determined by the regression model was significantly related to the real conflict effect(correlation coefficient 0.58,p < 0.001).Thus it is possible to predict the behaviour conflict effect using the functional connectivity between the relevant brain regions.With the development of science and techonology,transcranial direct current stimulation(t DCS),a non-invasive,directly altering cortical excitability is gradually applied to the cognitive control research.Numerous studies have shown that stimulation of the left dorsolateral prefrontal cortex(DLPFC)influences cognitive control including the working memory performance and emotional processing.Different polarity stimulation has different effect.However,the influence of t DCS on conflict control,another important component of cognitive control,is far more clear.Thus the second purpose of this thesis was to explore the effect of left DLPFC brain stimulation on the conflict effect.Participants were divided into two groups receiving either anodal or cathodal stimulation.Each group included two conditions,receiving either real or sham stimulation.The current was 1m A lasting 20 min.All participants performed the modified Stroop task before and after the t DCS.The results of the three-factor repeated measure analysis of variance showed that:(a)reaction time and accuracy were super in the post-t DCS test than in the pre-t DCS test;(b)in the anodal group but not the cathodal group,stimulation over the left DLPFC reduced the conflict effect.Our findings indicate that regardless of the polarity of the stimulation,cognitive control in the post-t DCS test is better than the pre-t DCS test.Only in the anodal-stimulation condition,perform t DCS over the left DLPFC enhance cognitive control.We surmise that the anodal stimulation to the left DLPFC may reduce the conflict effect by enhancing the task-relevant information processing.Further studies are needed to explore the exact mechanism of the brain stimulation effect on the conflict effect as well as the treatment effect on the conflict-related cognitive disorders based on the f MRI/t DCS experiment.