Experimental investigation of self-inflicted versus other-inflicted injury behaviour in individuals with borderline personality disorder.

Introduction: Non-suicidal self-injury (NSSI) is found in over 70% of patients with Borderline Personality Disorder (BPD). The most common method is cutting, which is often used to reduce high levels of aversive tension under stress. Recent studies have shown that pain during injury is a major factor reducing this stress. This report focuses on the question, whether the stress relieving effect of a sharp pain stimulus is different, when the patient herself is inflicting the stimulus on the forearm.

Methods: 86 patients with BPD participated in this study. Stress was induced with a personalized script, followed by a non-invasive pain stimulus with a blunt blade, either self-inflicted or inflicted by the experimenter. Subjective (arousal, urge for NSSI, pain intensity) and objective (heart rate) parameters were measured to evaluate stress and pain. Group differences were analysed using hierarchical linear modelling.

Results: Pain intensity, arousal and the urge for NSSI were similar under both conditions. The initial decrease in heart rate following the pain stimulus was significantly larger when the stimulus was applied by the experimenter and was delayed by a few minutes in the self-inflicted condition.

Conclusions: In this experimental setting, the perspective of pain application (self vs. other) had no differential influence on either NSSI, pain intensity, or stress level. The stronger initial decrease in heart rate in the other-inflicted group during the stimulus may be due to the lack of active physical involvement in the procedure, which could have delayed the decrease of heart rate in the self-inflicted group.