Increased salivary oxytocin correlates with lower self-reported interoceptive accuracy in functional neurological disorders.

Introduction: Functional Neurological Disorder (FND) is shaped by psychosocial stress, early adversity, and neuroendocrine dysregulation. Oxytocin (OXT), a hormone central to stress regulation and interoception, remains largely unexplored in FND. Methods: In this cross-sectional study, salivary OXT was assessed at four timepoints across 87 participants (42 FND and 45 sex-age-matched healthy controls), including appetite and satiety and hormonal factors (intake of hormonal contraception or menstrual cycle phases) as covariates. Self-reported interoception, attachment style, childhood trauma and sexual functioning were assessed allowing analysis for association. Results: Patients with FND exhibited higher OXT concentrations (averaged across four timepoints: d = 0.55, p = 0.031), which remained when controlling for covariates. Appetite and satiety specifically modulated OXT levels at different timepoints, underlying the group difference after lunch (p = 0.006) and at the end of the study visit (p = 0.035). Self-reported interoceptive accuracy was negatively correlated with OXT (r = -0.31, p = 0.014) and insecure attachment was positively correlated with OXT in controls (r = 0.42, p = 0.005), but not in FND. No associations of OXT and childhood trauma or sexual functioning reports were found. Discussion: The elevated salivary OXT levels observed in patients with FND may reflect a dysregulated or compensatory neuroendocrine response. The combination of higher OXT and lower self-reported interoceptive accuracy suggests that OXT may be upregulated as an attempt to modulate bodily stress or restore homeostatic balance. The absent association of OXT with attachment style in FND specifically supports its role in dealing with socio-affiliative stress.