I found this article from the National Institute of Mental Health and thought it was interesting. It's an older article from 2008. As I read more current articles maybe I will eventually compare/contrast them all to see how research has changed over the past few years, or show how it continues to support developing theories.
Emotion-Regulating Circuit Weakened in Borderline Personality Disorder
Grey Matter Changes Linked to Runaway Fear Hub
Patients with borderline personality disorder had significantly lower density of grey matter, the brain's working tissue, in the anterior cigulate cortex, an area (yellow, at right) that regulates the brain's fear hub (below). MRI scan data shows the difference between patients and controls.