Neural Mechanism Of Motivational Anhedonia In Adolescents With Depression Inclination

Depression is a global and common disease and different patients may have different depressive levels.Especially major depressive disorder will seriously affect the daily life and make patients in the pain.When it is the most severe,depression can make patients commit suicide.Having its complex causes makes depression appear constantly new progress of neural mechanism research.In order to detect and intervene depression at an early stage,the study about the neural mechanism of depression inclination provides a theoretical basis for the early stage of the disease.The research on adolescent depression provides the basis for the neural mechanism of depression from the point of age of onset.Therefore,the study of neural mechanism in adolescents with depression inclination provides theoretical support for the neural mechanism of early depression.Anhedonia,as the core feature of depression,has become the focus of research,but it has different classifications which make depressive anhedonia research more difficult.Generally anhedonia researches are included in the process of reward processing.Although some studies have explained the motivational factors involved in reward processing,the brain mechanism by which motivational anhedonia effects reward processing is still unclear.In the process of reward processing,motivation is mainly reflected in the stage of expectation and decision making.However,in order to explore how motivational anhedonia influences reward processing,delay discounting task(DDT)without effort motivation and expectation motivation could be selected.Moreover,adolescence is a sensitive period of reward processing and anhedonia.Therefore,firstly this article used questionnaires and behavioral experiment to measure depressive levels on adolescents with depression inclination and healthy control group in late adolescence,then combined with functional magnetic resonance imaging(fMRI)experimental results and functional connectivity analysis,correlation analysis method to explore the neural mechanism of motivational anhedonia in adolescents with depression inclination.In the first experiment,depressive level and motivational anhedonia in the depression inclination group and the control group were measured by Beck Depression Inventory and Motivation and Energy Inventory,and then two groups completed delay discounting task for behavior experiment.After that delay discounting rate of per participant was calculated,and the difference between the depression inclination group and the control group on delay discounting rate was compared,including the correlation between delay discounting rate and questionnaire scores.Delay discounting rate of per participant was the basis of calculating the experimental materials for fMRI experiments.The results of questionnaires showed that there were significant differences between the depression inclination group and the control group in depressive level and motivational anhedonia.The results of the behavior experiment showed that the average delay discounting rate of the depressioninclination group was greater than that of the control group,but did not reach the significant level.The participants with depression inclination were also more likely to choose immediate rewards,as previous studies have shown.There was no significant correlation between delay discounting rate and questionnaire scores in participants with depression inclination.In the second experiment,delay discounting rate of per participant in the first experiment was used to calculate the experimental materials for self in fMRI experiment,and then the participants were asked to complete the delay discounting task during the scanning period,and finally the experimental results were analyzed.The results of activative brain regions in the depression inclination group and the control group showed that the activative intensity of the subcallosus gyrus and right amygdala in the depression inclination group with immediate rewards in the DDT was higher than that in the control group.The activative intensity of right putamen and left middle frontal gyrus in the depression inclination group was higher than that in the control group.In the choice of immediate reward comparing with delayed reward,the activative intensity of the right inferior parietal lobule and the right supramarginal gyrus in the depression inclination group was greater than that in the control group.The functional connection between the region of interest and the whole brain in the depression inclination group and the control group showed that the greater level of motivational anhedonia,the greater intensity of the functional connection between the posterior cingulate gyrus and the whole brain.Moreover,the results of functional connection between regions of interest showed that the direction of functional connection in the right supramarginal gyrus and posterior cingulate gyrus was positive in the depression inclination group comparing with the control group.The results of the correlation analysis between the scores of motivational anhedonia questionnaire and the signal strength of functional connection between the regions of interest and the whole brain showed that the intensity of functional connection between the right supramarginal gyrus and the right posterior cingulate gyrus could predict the level of motivational anhedonia in the depression inclination group and the control group.The results show that there may be no significant difference in delay discounting rate between adolescents with depression inclination and healthy controls.In the depression inclination group,the neural mechanism of motivational anhedonia influencing reward processing about delay discounting may be located in the right amygdala which is responsible for immediate reward,the left middle frontal gyrus which belongs to the control system,and the right supramarginal gyrus which is responsible for conflict monitoring.The level of motivational anhedonia can be predicted by the intensity of functional connection between the right supramarginal gyrus and the whole brain and between the right posterior cingulate gyrus and the whole brain.The overreaction of the right supramarginal gyrus and right posterior cingulate gyrus in reward processing about delay discounting suggests that these twobrain regions may be impaired in depression inclination individuals with anhedonia.These results provide important evidence for further understanding of the neural mechanism of anhedonia in depressive adolescents,which is of great significance for further intervention of depressive adolescents.