Altered brain activation patterns in dyssynergic defecation: Investigating neural mechanisms through task-based fMRI analysis

Dyssynergic Defecation (DD) is a functional disorder characterized by paradoxical contraction or insufficient relaxation of the pelvic floor muscles during defecation. While behavioral and physiological factors have been extensively investigated, the underlying central neural mechanisms remain inadequately understood. This study aims to elucidate the differences in brain activation patterns between individuals with DD and healthy controls (HC) during a simulated defecation task utilizing fMRI, thereby addressing the limited comprehension of its neural mechanisms. We recruited eight patients diagnosed with DD and ten HC participants. All subjects underwent task-based fMRI while engaging in a validated simulated defecation paradigm. Additionally, the Constipation Scoring System (CSS), the Patient Assessment of Constipation Quality of Life (PAC-QOL), and Montreal Cognitive Assessment (MOCA) were utilized to assess Clinical indicators. The fMRI data were preprocessed and analyzed employing a general linear model (GLM) to identify brain regions exhibiting significant activation during the task. Comparisons between groups were conducted, along with correlation analyses with Clinical indicators. The DD cohort displayed diminished activation in the right thalamus and right cerebellum (VI), whereas the HC group exhibited activation in the right cerebellum (VI) and the right inferior parietal lobule. Notably, the DD group demonstrated negative activation in several brain areas, including the left fusiform gyrus and left parahippocampal gyrus, when compared to HC. Correlation analysis indicated positive relationships between brain activation in specific regions, such as the right cerebellum (VI) and the left cerebellum (III), with CSS scores and symptoms of straining and incomplete evacuation. Individuals with DD manifest a distinct profile of dysfunctional brain activation during simulated defecation. These findings suggest a central neural pathophysiology characterized by impaired sensorimotor integration, excessive cognitive inhibition, and altered interoceptive processing. This provides a novel perspective for comprehending DD and may guide future neuromodulation-based therapeutic approaches.