Although
the cause of BPD is unknown, both environmental and genetic
factors are thought to play a role in predisposing patients
to BPD symptoms and traits. Studies show that many, but not
all individuals with BPD report a history of abuse, neglect,
or separation as young children. Forty to 71 percent of BPD
patients report having been sexually abused, usually by a non-caregiver.
Researchers believe that BPD results from a combination of individual
vulnerability to environmental stress, neglect or abuse as young
children, and a series of events that trigger the onset of the
disorder as young adults. Adults with BPD are also considerably
more likely to be the victim of violence, including rape and
other crimes. This may result from both harmful environments
as well as impulsivity and poor judgment in choosing partners
and lifestyles.
NIMH-funded neuroscience research is revealing brain mechanisms
underlying the impulsivity, mood instability, aggression, anger,
and negative emotion seen in BPD. Studies suggest that people
predisposed to impulsive aggression have impaired regulation
of the neural circuits that modulate emotion. The amygdala,
a small almond-shaped structure deep inside the brain, is an
important component of the circuit that regulates negative emotion.
In response to signals from other brain centers indicating a
perceived threat, it marshals fear and arousal. This might be
more pronounced under the influence of drugs like alcohol, or
stress. Areas in the front of the brain (pre-frontal area) act
to dampen the activity of this circuit. Recent brain imaging
studies show that individual differences in the ability to activate
regions of the prefrontal cerebral cortex thought to be involved
in inhibitory activity predict the ability to suppress negative
emotion.
Serotonin, norepinephrine and acetylcholine are among the chemical
messengers in
these circuits that play a role in the regulation of emotions,
including sadness, anger, anxiety, and irritability. Drugs that
enhance brain serotonin function may improve emotional symptoms
in BPD. Likewise, mood-stabilizing drugs that are known to enhance
the activity of GABA, the brain's major inhibitory neurotransmitter,
may help people who experience BPD-like mood swings. Such brain-based
vulnerabilities can be managed with help from behavioral interventions
and medications, much like people manage susceptibility to diabetes
or high blood pressure.
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