From local activity to effective connectivity: neuroimaging evidence of functional abnormalities in the inferior occipital gyrus in obsessive-compulsive disorder

Existing studies on obsessive-compulsive disorder (OCD) typically use single imaging metrics or resting-state functional connectivity, limiting insight into the directional brain information flow. Imaging data for 93 OCD patients and 96 healthy controls (HC) were analysed. Between-group differences in fractional amplitude of low-frequency fluctuations (fALFF) and regional homogeneity (ReHo) identified common discrepant brain regions, used as seed points for whole-brain effective connectivity (EC) analysis via granger causality. Compared to HC, patients with OCD exhibited reduced fALFF in the left inferior occipital gyrus (L_IOG) and postcentral gyrus, elevated fALFF in the left caudate nucleus, and reduced ReHo in the L_IOG and right calcarine sulcus. EC from the right caudate nucleus to the L_IOG was attenuated, while that from the right supramarginal gyrus to the L_IOG was enhanced. Furthermore, diminished connectivity was observed from the L_IOG to the right middle frontal gyrus, middle occipital gyrus, dorsolateral superior frontal gyrus, and postcentral gyrus (R_PoCG). Among them, fALFF value of the L_IOG and its EC value to the R_PoCG were positively correlated with OCD symptom severity. The L_IOG may function as a pivotal integrative node spanning sensorimotor and executive control networks, contributing to the pathological mechanisms of OCD.