Transcutaneous Vagus Nerve Stimulation (tVNS) for Borderline Personality Disorder (tVNS-BPD)

The goal of this clinical trial is to test the efficacy of transcutaneous vagus nerve stimulation (tVNS) in borderline personality disorder. The main question it aims to answer is:

• Is tVNS effective in acutely reducing emotional reactivity in borderline personality disorder?

Participants will be randomized to a single session of tVNS or sham-tVNS while going through an affect-inducing procedure. It will consist of the presentation of one neutral and three negative affect-inducing videos in sequence, each of which is followed by a post-induction period during which participants will rate the quality and intensity of their current self-reported emotions.

Researchers will compare the tVNS and sham tVNS groups to see if there is a difference in the intensity of the self-reported emotions between the groups.

The study will be a randomized, single-blind, sham-controlled trial. The goal of this clinical trial is to test the efficacy of transcutaneous vagus nerve stimulation (tVNS) acutely reduce emotional vulnerability and improve emotional regulation in borderline personality disorder. The main questions it aims to answer are:

* Is tVNS effective in acutely reducing emotional reactivity in borderline personality disorder?
* Is tVNS effective in acutely reducing baseline emotional arousal in borderline personality disorder?
* Is tVNS effective in acutely ease emotional recovery in borderline personality disorder?
* Is tVNS effective in acutely improve emotional regulation in borderline personality disorder?

The participants will be randomized to a single session of tVNS or sham-tVNS while going through an affect induction procedure. It will consist of the presentation of one neutral and three negative affect-evoking 4-minutes-long videos in sequence, each of which is followed by a 4-minutes post-induction period during which participants will rate the quality and intensity of their current self-reported emotions (post-induction ratings) and the perceived effectiveness in managing their emotions during the video presentation. The rating of the current self-reported emotions will be repeated after every post-induction period (recovery ratings).

To test the difference in negative emotional arousal at every stage and the perceived effectiveness in managing emotions between the tVNS and sham tVNS groups, mixed models with individuals as random effects will be used. These models will take into account the repeated measurements of the same individuals at baseline, pre-induction, post-induction, and recovery.

Eligibility Criteria:
Inclusion Criteria:

* Swedish-speaking and able to provide informed consent to participate in the study
* Female and between the ages 18 and 50 years old.
* Current DSM-5 (Diagnostic and statistical manual of mental disorder-5) diagnosis of BPD based on the Structured Clinical Interview for DSM-5 Personality Disorders (SCID-5-PD)
* Capable (in the Investigator's opinion) and willing to comply with all study requirements.

Exclusion Criteria:

* Any unstable medical and/or neurological condition
* Currently pregnant
* Any significant neurological disorder or condition likely to be associated with increased intracranial pressure or cognitive impairment (e.g., a space occupying brain lesion, a history of stroke, a cerebral aneurysm, a seizure disorder, Parkinson's disease, Huntington's chorea, multiple sclerosis)
* Current diagnosis of delirium, dementia or another cognitive disorder secondary to a general medical condition
* Established diagnosis of a developmental and neuropsychiatric disorder (e.g. Down syndrome, autism-spectrum disorder, ADHD)
* Non-correctable clinically significant sensory impairment (i.e., cannot hear or see well enough to complete the affect induction procedure, follow and answer the survey instructions and questions)
* Alcohol or substance use disorder (relating to opioids, cocaine, amphetamine or benzodiazepine) currently or within the past 1 month
* Daily treatment with antiepileptics (e.g., carbamazepine, gabapentin, lamotrigine, levetiracetam, pregabalin, sodium valproate, topiramate) or benzodiazepines (last dose over 7 days before the screening)
* Alcohol or substance use disorder (relating to opioids or cocaine) currently or within the past 1 month
* Intracranial implant (e.g., aneurysm clips, shunts, stimulators, cochlear implants, or electrodes) or any other metal object within or near the head, excluding the mouth, that cannot be safely removed
* History or diagnosis of bipolar or chronic psychotic disorder (e.g., schizophrenia, schizoaffective disorder).