Furthermore, in this study, the majority of these regions with GMD changed such as the ACC, insula and PFC, belong to the homeostatic afferent processing network. Our previous PET-CT study indicated that, compared to the HS, the FD patients showed a higher glycometabolism in the regions of the homeostatic afferent processing network especially the ACC, insula and OFC. Our DTI study also demonstrated that FD patients showed altered white matter tracts which were connected with regions of the homeostatic afferent processing network, including right external capsule, right sagittal stratum, right superior longitudinal fasciculus, corpus callosum, corona radiata, right retrolenticular part of the internal capsule, and right posterior thalamic radiata. Thus, we predicted that the structural and functional changes in the homeostatic afferent processing network might be an important character of FD patients. Many studies suggested that psychological factors might be one of the possible causes of FD. It was reported that FD patients had significantly higher levels of psychiatric illness than the HS and the patients with organic dyspepsia. Some studies demonstrated that anxiety seemed to be related to abnormal antral retention of food, and that depression was related to the abdominal fullness severity. Furthermore, limited data showed that the meal-related FD patients were more likely to suffer with psychopathology. Recently, using functional neuroimaging techniques, people found that psychological factors were significantly associated with cerebral dysfunction of FD patients. For example, Van Oudenhove L, et al. reported that anxiety was negatively correlated with pACC and MCC, and positively correlated with dorsal pons activity in FD patients, and that abuse history was associated with differences in insular, prefrontal, and hippocampus/amygdala activity. In this study, the VBM results indicated that many regions in emotional arousal circuitry of meal-related FD patients showed a significant reduction in GMD. The present results demonstrated that these cerebral microstructural changes in the meal-related FD patients are in part related to the comorbidities of depression and anxiety. The insula, considered as one of the key regions of ��gut-brain communication��, plays a crucial role in processing and modulating visceral sensory, pain, emotion, and maintaining homeostasis. Activations in the insula can be found in nearly all reported FGIDs studies, regardless of the study paradigm and analysis methods. Some study demonstrated that the insula processed the interceptive signals of fullness produced by gastric distention. Our previous PET-CT study indicated that, compared to the HS, the meal-related FD patients showed a higher glycometabolism in the insula, and that the abnormal hyperactivity of the 
insula was significantly related to the symptom severity of FD patients. Furthermore, a MRI study on IBS patients showed a cortical thinning in the insula.