Glenn Close’s unforgettably vivid portrayal in the movie Fatal Attraction gave viewers a front-row look at the damaging mental illness known as borderline personality disorder (BPD). By itself, this ailment accounts for up to 10 percent of patients under psychiatric care and 20 percent of those who have to be hospitalized. The defining characteristic is pervasive instability in the patient’s life, especially in relationships. People who suffer from BPD also have difficulty controlling their impulses and regulating their emotions. Their behavior exerts a tremendous toll not only on themselves but also on their friends and colleagues, as well as on the health care system.
Despite the importance of this disorder, surprisingly little is known about what brain mechanisms might underlie it. Over the past few years, however, scientists have found intriguing hints. Structural imaging studies have indicated, for example, that parts of the brain’s limbic system, which regulates various aspects of emotion, are abnormally small in patients with BPD, and the areas that appear most reduced in volume govern negative moods. Investigations of functional abnormalities show that these same limbic areas—including the amygdala—tend to be hyperactive. Some researchers theorize that the smaller size of limbic structures reflects a loss of inhibitory neurons, which might mean these patients’ brains have a weaker rein on behavior and negative emotions, leading to impulsivity and overly negative reactions to events.