Neuroimaging Study On Brain Resting State Networks’ Functional Connectivity Affected By Obesity And Bariatric Surgery

Nowadays,due to unhealthy eating behaviors and lack of exercise,people’s long-term surplus of calories in the body is transformed to the excessive accumulation of fat leading to obesity.In recent years,the incidence of obesity has increased rapidly worldwide,and obesity has become a severe public health problem globally.Clinically,bariatric surgery is an effective treatment for obesity in both short-and long-term.Neuroimaging studies have found that obesity causes structural and functional disorders of the brain.Bariatric surgery can reverse the abnormal structure and function of the brain in obese people and make them go back to having a normal weight.Previous studies about obesity and bariatric surgery mainly study the abnormal functional connectivity(FC)related to obesity from the local brain area;however,the abnormality of the obesity-related resting state networks(RSNs)and the abnormal interaction between the networks from the perspective of a large-scale network have been less studied.Therefore,in the current study,independent component analysis(ICA)and functional network connectivity(FNC)were used to investigate the changes of functional connectivity and interaction between RSNs in obese patients before and after bariatric surgery from the perspective of networks based on functional magnetic resonance imaging(f MRI)and diffusion tensor imaging(DTI).(1)For the changes in functional connectivity in the basal ganglia network caused by obesity,a study was performed in 35 normal-weight subjects(NW)and 32 patients with obesity(OB).Results showed that compared to NW,OB showed significant reduced(FC)strength in the caudate nucleus(CAU)in the basal ganglia network,and the seed-based FC analysis found that FC between CAU and dorsolateral prefrontal cortex(DLPFC)was reduced significantly in OB.Correlation analysis between clinical measures and imaging data found that the reduced FC of CAU-DLPFC was negatively correlated with craving for high-calorie food.The FC changes and the craving-related areas of the CAU and DLPFC were selected as seed points to analyze the changes in white matter fiber connections behind the functional connectivity induced by obesity.Therefore,based on the DTI,the results found that the FA value of the white matter fiber connection between the left CAU and left DLPFC was significantly decreased compared to NW using probabilistic tractography.These results suggest that the abnormality of reward(CAU)– inhibitory-control(DLPFC) circuit caused by obesity(including structure and function)leads to the disordered reward processing of food and lack of control of feeding behaviors of the brain.(2)Based on the above mentioned research about a single basal ganglia network,after adding subjects,the study about alterations in FC within and interactions between RSNs caused by obesity on 35 OB and 35 NW was carried out.Results showed that compared to NW,OB showed reduced FC strength in brain regions associated with self-referencial function(VMPFC/PCC)in the default-mode network(DMN),reward processing(dACC)within the salience network(SN),executive-control(DLPFC/ANG)within the executivecontrol networks,and increased FC strength in the brain region related to interoception(INS).Correlation analysis between clinical measures and imaging data found that reduced FC strength of the d ACC was negatively correlated with craving for food-cues,FC strength of the left DLPFC was negatively correlated with Yale-Food-Addiction-Scale scores,and increased FC strength of the right INS was positively correlated with craving for high-calorie food-cues.Functional network connectivity analysis based on ICA found that compared to NW,OB also showed increased FC between SN and ECNs driven by altered FC of the bilateral INS and ACC-ANG.The above results indicated that alterations in FC within and interactions between RSNs might contribute to the high incentive value of food(craving),lack of control of over eating(compulsive overeating)and increased awareness of hunger(impaired interoception)in obesity.(3)ICA was used to study alterations in FC within and interactions between RSNs caused by bariatric surgery.Results showed that bariatric surgery increased the FC strength of CAU related to reward processing in the basal ganglia network,reversed the altered causal effect between SN and DMN in obese patients,and enhanced the functional connectivity between sensory brain regions(INS)and self-referential brain regions(VMPFC).These results suggest that bariatric surgery enhances the FC of brain regions associated with regulating appetite-related reward and hunger awareness in obese patients,and improves the disordered interactions between RSNs of the brain to restore normal coordination.In this paper,the study revealed an obesity-related functional interaction mechanism between RSNs and mechanism of regulating function of RSNs through bariatric surgery from the perpective of the a large scale network,providing the imaging evidence for the pathogenesis of obesity and regulation mechanism of bariatric surgery.