Altered Interoceptive Predictive Coding in Functional Neurological Disorders

Interoception, the processing of internal bodily signals, has been linked to the pathophysiology of Functional Neurological Disorder (FND), along with the theoretical concept of altered predictive coding (PC). FND symptoms such as sensory-motor dysfunction may arise from disrupted integration of sensory input and predictions. However, PC in the modality of interoception has not yet been investigated in FND. Using a PC paradigm, the cardio-audio synchronization task measured electrophysiological responses to the heartbeat during omitted sounds that were temporally locked to the heartbeat (synchronous condition) or not (asynchronous control condition). Patients with mixed FND symptoms (N = 36) were compared to sex- and age-matched healthy controls (HC: N = 42) by contrasting synchronous and asynchronous heartbeat-evoked potentials during omissions using cluster-based permutation statistics. We further tested associations with self-reported interoceptive variables and assessed whole-scalp main and interaction effects in global field power (GFP) and topography. Patients with FND showed no cluster-level differences between conditions, whereas we identified a central cluster difference in HCs. The interoceptive-specific contrast (synch-asynch difference waves) differed between groups and correlated with interoceptive self-report but only when tested across groups (r = -0.33, p = 0.012). In this paradigm, group-by-condition interactions in topography identified the insula as the most probable source of differences. These interactions occurred before those identified in GFP analyses, suggesting that differential networks emerge first, followed by changes in overall activity strength. These results indicate that patients with FND use different neural mechanisms for interoceptive PC (i.e., precision-weighted prediction errors in interoception-guided predictions) than HCs. Patients with FND showed no difference in interoceptive PC, suggesting a dysfunctional interoceptive system. Together, these findings suggest that interoceptive-cued regularity processing in FND is characterized by altered early network recruitment, followed by differences in overall signal strength, potentially reflecting a disrupted progression of interoceptive PC.