Transcutaneous auricular vagus nerve stimulation modulates emotional vulnerability in borderline personality disorder: a single-blind, sham-controlled study

Borderline personality disorder (BPD) is characterized by pervasive emotional vulnerability, yet the biological mechanisms underlying exaggerated reactivity, heightened sensitivity, and delayed recovery remain insufficiently understood. Building on evidence of alterations in autonomic and interoceptive processing in BPD, we introduce the Interoceptive Threshold Model, which proposes that emotional vulnerability reflects a lowered threshold for detecting and interpreting autonomic fluctuations. In this randomized, single-blind, sham-controlled experiment, 34 female outpatients with BPD received a 45-min session of active or sham transcutaneous auricular vagus nerve stimulation (taVNS) while completing a validated emotional video paradigm. Participant ratings of negative affect and autonomic indices (heart rate, heart rate variability (HRV), electrodermal activity) were assessed across reactivity (baseline to post-induction), sensitivity (baseline to pre-induction), and recovery (post-induction to recovery) phases. During affect induction, taVNS compared with sham taVNS attenuated emotional reactivity and enhanced autonomic flexibility, as indicated by increased HRV and electrodermal response frequency, without significantly altering heart rate or peak amplitude. Compared with sham, taVNS reduced pre-induction negative affect and increased HRV, suggesting lower emotional sensitivity. During recovery, taVNS facilitated steeper declines in phasic sympathetic activity. These findings demonstrate that taVNS modulates all three components of emotional vulnerability in BPD and support a mechanism of interoceptive recalibration rather than autonomic suppression. This study provides the first experimental evidence that vagal-afferent stimulation can alter interoceptive thresholds in BPD, identifying a promising mechanistic target for future interventions.