Introduction

Obesity involves aberrant multiple brain networks. Bariatric surgery effectively intervenes, directly and sustainably improving somatic function in obesity. However, its contribution to reorganizing obesity-associated resting-state network connectivity remains elusive.

Methods

Thirty obese patients undergoing laparoscopic sleeve gastrectomy were recruited at Xiangya Hospital, Central South University, China. Patients with psychiatric/neurological disorders or prior abdominal surgery were excluded. Identical pre- and post-surgery MRI scans were completed 3 months after sleeve gastrectomy. The study was approved by Xiangya Hospital's Ethics Committee and registered at the Chinese Clinical Trial Registry. It adhered to the principles of the Helsinki Declaration. All participants were informed of the study's nature and provided written informed consent. After 12-hour overnight fasting, all participants underwent MRI scans between 6-8 am. Identical measurements were taken at baseline before surgery and 3 months after surgery, with all surgeries performed by the same surgeon (GJ) (Table 1). Images were preprocessed using SPM. Independent component analysis using GIFT software was applied to the images. 10 functional networks were obtained: anterior and posterior default mode networks (aDMN and pDMN), left and right fronto-parietal networks (lFPN and rFPN), salience network (SN), dorsal attention network (DAN), sensory motor network (SMN), auditory network (AUN), primary and higher visual networks (pVN and hVN). Shown in Figure 1.

Results

hVN-lFPN, hVN-SMN, AUN-pDMN, AUN-DAN, pVN-aDMN, pVN-SMN, pDMN-SN, aDMN-DAN, and SMN-DAN connectivity showed statistically significant differences, with greater connectivity post-surgery compared to pre-surgery. Shown in Figure 2 and Table 2.

Discussion

Bariatric surgery can improve resting-state brain functional network connectivity.
We found improved connectivity of hVN-lFPN, hVN-SMN, pVN-aDMN, and pVN-SMN after bariatric surgery. The visual system processes visual information, including primary (V1) and higher-order areas involved in object recognition and motion perception. It functions in food cue processing. Geha et al¹. found increased visual cortex whole-brain connectivity in obese vs normal-weight individuals at rest and when drinking milkshakes. Frank et al² found that after RYGB surgery, lower liking/wanting and eating behavior scores correlated with higher activation in visual, prefrontal, interoceptive, motor, memory, and gustatory regions. Ten Kulve et al³ found decreased reward region activity after RYGB when viewing/tasting food with GLP-1R blockade, increasing activity to food cues. The left fronto-parietal network (L-FPN) exerts broad control over brain information flow, underlying executive functions like goal-directed cognition, working memory, inhibition, and task-switching. The fronto-parietal network is highly associated with eating behavior^4,5 and strongly correlates with BMI⁶. The sensorimotor network underlies motor control and links to reward systems. Disruption can reduce motivation for energy expenditure. Obese individuals may have motor difficulties and altered body image, influencing food and activity behaviors. Decreased connectivity within the SMN has been found in obese patients⁷.
Connectivity of pDMN-SN and aDMN-DAN was enhanced after compared to before surgery. The DMN includes the medial prefrontal, posterior cingulate, medial temporal, and angular gyri. Studies show increased bilateral wedge frontal lobe and decreased right posterior cingulate cortex functional connectivity within default and temporal networks in obesity⁸. The salience network includes the dorsal anterior cingulate, insular, and orbital frontal cortices, involved in emotional arousal, reward sensitivity, and decision making⁹. In the SN, obese participants showed increased functional connectivity strength of the nucleus accumbens at resting state fMRI, and may lead to binge eating through an imbalance between autonomic processing and reward processing of food cues¹⁰. The dorsal attention network (DAN) consisting of the frontal eye fields (FEF) and intraparietal sulcus (IPS) showed decreased interoceptive/attentional network and increased visual/salience network functional connectivity in overweight compared to normal weight individuals¹¹.
We found that the connectivity between the auditory network (AUN) and posterior default mode network (pDMN), and between AUN and dorsal attention network (DAN) was enhanced after bariatric surgery. The postprandial increase in GLP-1 (pre- to post-surgery) was associated with reduced RYGB surgery brain activation in the temporal and parietal lobes, and enhanced stimulation of the right ventromedial prefrontal cortex/cingulate, suggesting these attentional and inhibitory regions contributed to augmented satiety signaling after surgery¹².

Discussion

In summary, we found that bariatric surgery induced significant rsFC changes across multiple networks in obese patients. Our findings indicate that functional connectivity changes after bariatric surgery in obese patients go beyond interoceptive, default mode, salience, and attentional networks, extending to visual and auditory networks. We speculate these changes may represent adaptive modulatory mechanisms in visual, auditory, interoceptive, motor, attentional, salience, and default mode networks during weight loss. These network connectivity changes elucidate the role of functional homeostasis rebalancing triggered by bariatric surgery, and may help clarify the underlying brain mechanisms during weight reduction.

Acknowledgements

No acknowledgement found.