Exploring brain activity differences in functional constipation using fNIRS: a case-control study

BACKGROUND: Functional constipation (FCon) involves central nervous system dysregulation, particularly in brain regions responsible for visceral sensation, emotional processing, and autonomic control. Using functional near-infrared spectroscopy (fNIRS), we examined brain activity alterations in FCon patients to elucidate brain-gut interactions. METHOD: Patients with constipation meeting Rome IV criteria were recruited from Sir Run Run Shaw Hospital, while healthy controls were enrolled from the local community. The cortical regions of interest (ROIs) included the prefrontal cortex (PFC), dorsolateral prefrontal cortex (DLPFC), broca's area, primary motor cortex (M1), supplementary motor area (SMA)/premotor cortex (PMC), and primary somatosensory cortex (S1). Participants were monitored during resting state and three defecation-related tasks: imagined defecation, simulated defecation and anal sphincter contraction. Functional connectivity (FC) strength and regional brain activation (HbO concentration changes) were compared between groups and across tasks. RESULT: 64 patients and 64 healthy controls (50% females each) were included. There was no significant difference in average FC between groups (P = 0.757). In both groups, simulated defecation and anal sphincter contraction activated most ROIs more strongly than imagined defecation (P < 0.05). In healthy controls, anal sphincter contraction elicited significantly lower HbO than simulated defecation in the left Broca's area (P < 0.05); no significant differences between these two tasks were found in the FCon group. No significant between-group differences in HbO were found during any task. During imagined defecation, FCon patients showed a trend toward lower HbO across most ROIs, most notably in the right M1, with comparable levels in the right PFC. During simulated defecation, a similar trend of lower HbO in sensorimotor ROIs was observed alongside numerically higher HbO in the right PFC/DLPFC. During anal sphincter contraction, they showed numerically higher HbO across all ROIs. Progression curves further revealed a linear increasing pattern in FCon patients across tasks, contrasting with task-appropriate modulation in healthy controls. CONCLUSION: This first fNIRS study reveals task-specific cortical dysregulation in FCon. Although between-group differences were not statistically significant, these trends and dynamic patterns identify sensorimotor and prefrontal cortical targets for future neuromodulation therapies. Trial registration ChiCTR2500104882.