Functional Connectivity Gradients Reveal Altered Hierarchical Cortical Organization in Functional Neurological Disorder

ABSTRACT Background Neuroimaging studies of functional neurological disorder (FND), a condition at the intersection of psychiatry and neurology, often rely on discrete connections or parcellations that may obscure the brain’s functional network architecture. This study applied a gradient-based approach to examine macroscale cortical organization in FND. Methods We analyzed resting-state functional magnetic resonance imaging (fMRI) data from 64 patients with mixed FND (FND-mixed), 61 age- and sex-matched healthy controls (HCs), and 62 psychiatric controls (PCs) matched on age, sex, depression, anxiety, and post-traumatic stress disorder (PTSD) severity. Functional connectivity gradients were computed to capture dominant axes of cortical organization. Between-group comparisons were conducted for the top three gradients, and associations with symptom severity were investigated. Subtype-specific patterns in functional motor disorder (n=49) and functional seizure (n=24) were also examined. Analyses controlled for age, sex, and antidepressant use, and were post-hoc adjusted for depression, anxiety, and PTSD-severity, and for childhood maltreatment. Results The FND-mixed group showed alterations across all three gradients relative to HCs and PCs. Gradient 1 revealed increased values in sensorimotor regions, reflecting a shift toward more association-like connectivity. Gradient 2 showed altered differentiation between sensory systems. Gradient 3 exhibited reduced functional separation between representational and modulatory regions, with prominent shifts in the anterior cingulate cortex. Several regions displaying between-group differences also showed correlations with FND and somatic symptom severity. Analyses revealed overlapping and distinct patterns across subtypes. Conclusions We provide novel evidence of atypical hierarchical brain organization in FND, highlighting gradient-based approaches for identifying mechanistically-relevant altered functional brain organization.