Within-group variation in interoceptive bias between patients with somatic symptom disorder on a heart rate discrimination task

The persistence of physical symptoms, such as pain, fatigue, and dizziness, has been linked to altered interoception, but the mechanisms remain unclear. This study used a novel psychophysical heart rate discrimination task and self-report measures of interoceptive sensibility and awareness to investigate interoceptive deficits in patients with somatic symptom disorder (SSD) and healthy controls from a predictive processing perspective. Both groups underestimated their heart rate, with no differences on sensory precision and discriminability. Patients with SSD reported lower decision confidence and showed higher between-person variation in interoceptive bias, either under- or overestimating their heart rate. Self-report data revealed reductions on regulatory and trusting facets of interoceptive sensibility, related to symptom reporting. Through a predictive processing lens, the pattern found is consistent with heterogeneous priors combined with higher-level cognitive “immunization” that resists disconfirmatory evidence. This study highlights the need for a broader understanding of interoception in persistent physical symptoms, integrating both higher-order and lower-order interoceptive mechanisms.