Respiratory sensitivity is reduced in functional neurological disorder and associated with higher somatoform dissociation.

Abnormal interoception-the processing of internal bodily signals-has been increasingly recognized as a key factor in the pathophysiology of functional neurological disorder. While evidence suggests reduced cardiac interoceptive accuracy in functional neurological disorder, other interoceptive domains, such as respiratory processing, remain largely unexplored. Here, we introduce a novel respiratory resistance sensitivity task to assess respiratory interoception and metacognition in functional neurological disorder. Additionally, we investigate the relationship between respiratory interoception and other interoceptive or clinical variables, including somatoform dissociation as a potential inverse correlate of interoception. Using the respiratory resistance sensitivity task, respiratory interoceptive sensitivity and metacognition were assessed, along with the response time and the decision precision for identifying the obstructed breath in the respiratory task in patients with mixed functional neurological disorder (N = 43) and age- and sex-matched healthy controls (N = 48). Drift diffusion modelling was applied to response times and discrimination decisions to assess sensory evidence accumulation. Additionally, interoceptive self-reports (multidimensional assessment of interoceptive awareness and the interoceptive accuracy scale) were collected. Associations between interoceptive measures, symptom severity, and the Somatoform Dissociation Questionnaire were analysed. Patients with functional neurological disorder showed reduced respiratory sensitivity (P  = 0.032, d = 0.47) and interoceptive self-report scores (P  = 0.0004, d = 0.79 and P  = 0.018, d = 0.65, respectively) compared to controls, whereas metacognition and decision precision did not differ between groups. In the functional neurological disorder group, respiratory sensitivity and metacognitive performance were negatively associated with somatoform dissociation scores (r = -0.38, P = 0.011 and r = -0.36, P = 0.017, respectively). While no group difference was found for the response time, we did identify a negative correlation with response time and respiratory sensitivity (r = -0.27, P = 0.013) and reduced drift rate in patients with 89% posterior probability. Further, perceived breathlessness (r = -0.24, P = 0.026) was negatively associated with the task performance. This study provides first evidence of impaired respiratory interoception in patients with functional neurological disorder. We were able to demonstrate a moderate-sized group difference in a large cohort, using a valid respiratory task, that is, associated with clinical variables such as self-reported severity of somatoform symptoms. Further, reduced drift rates for patients with functional neurological disorder indicated less efficient sensory evidence accumulation, while indifferent boundary separation indicated preserved decision caution. These novel insights into respiratory interoception in functional neurological disorder suggest it may represent a therapeutic target for future investigation.