A new study provides an illuminating look into the brains of sufferers.
By Andreas Meyer-Lindenberg
mental illnesses. By itself, this severe mental illness accounts for up
to 10 percent of patients in psychiatric care and 20 percent of those
who have to be hospitalized. The defining characteristic of BPD is a
pervasive instability in the patient’s life, especially when it comes
to interpersonal relationships. BPD patients also have difficulty
controlling their impulses and regulating their emotions. Close
relationships of patients are often tumultuous and compromised by
highly unpredictable behavior that can leave others baffled, angry and
frightened. This behavior exerts a tremendous toll not only on those
afflicted with the illness, but also on their social network and the
health care system. (A well known, if dramatized, example is the
character Glenn Close played in the movie Fatal Attraction.)
Surprisingly, despite the importance of this disorder, little is yet
known about what brain mechanisms might underlie it. In a recent paper in the journal Science, Brooks King-Casas and colleagues at Baylor College of Medicine provide an illuminating look into the brain in people suffering from BPD.
In this study, patients and healthy controls played a game in which
money is exchanged between an investor, who decides how much to invest,
and a trustee, who decides how much of the investment, which is tripled
during the transfer, to repay. For example, if the investor decides to
invest $10, then the trustee has $30 to divide ($10 x 3). Although this
game is at first glance about money, it is really about the development
of trust.
If both players cooperate, both benefit from the exchange, much more so
than if the investor keeps most of the money for him- or herself.
This trade requires a degree of trust
between the players that is built up through repeated fair offers,
however. An investor who does not trust the other player will not put
in much money. This small offering is exactly what happened at the end
of games with BPD trustees, indicating that they had difficulties
establishing and maintaining cooperative relationships. In contrast,
players without BPD (they were the healthy “control” subjects) still
had high levels of at the end of the game. They accomplished such
amounts through a “coaxing” strategy, in which wary investors
transferring small amounts of money were encouraged by generous
returns, which signal trustworthiness. The study found that healthy
players used this strategy twice as often as BPD subjects.
Investing in Trust
To find out why patients behaved this way, the researchers used
neuroimaging (fMRI) to study brain activation of trustees confronted
with a small investment, which usually signals a lack of trust on the
investor side. Although most healthy trustees would respond to such a
move with the coaxing strategy—is a demonstration of their own
trustworthiness—patients with BPD did not. Furthermore, the fMRI scans
revealed a crucial difference between BPD subjects and healthy players.
In healthy subjects, a region of the brain called the anterior insula
seemed to neurally represent the investment level, so that small
investments corresponded to large activation and vice versa. In BPD
patients, however, no such correlation existed. As expected from
previous work, this same brain area also represented the amount of
money subjects were about to repay to the investor, so that a large
activation in the insula predicted a small payment from the trustee.
Strikingly, however, this correlation was now the case in both subjects
with BPD and healthy controls. In other words, although healthy
controls had insula activations both to “distrustful” offers from
investors and “stingy” repayments, subjects with BPD represented only
their own actions. Their impairment seemed to selectively concern the
representation of the other player.
The anterior insula has long been associated with the representation of uncomfortable bodily sensations, such as pain.
In addition, many studies have since shown that this area also strongly
reacts to adverse or uncomfortable occurrences in social interactions,
such as unfairness, excessive risk, frustration or impending loss of
social status. This body of work suggests that the anterior insula
tracks information about the intentions and behavior of others and
colors them with a feeling of discomfort. If true, then one reason BPD
subjects may be impaired in maintaining cooperation is because they
lack the “gut feeling” (corresponding to the anterior insula signal)
that there is a problem with the relationship. Because they can’t
detect the breakdown of trust, they are less likely to trust others at
all.
A Network Problem?
This exciting finding prompts many new questions. The first is, What
causes this abnormal brain activity? Most research indicates that BPD
commonly arises from a combination of genetic predisposition and severe
early child trauma. Not everyone traumatized as a child develops BPD,
but it could be that a combination of risk genes makes the impact of
trauma on the developing brain more severe and enduring. It would be of
high interest to determine whether such genetic variants, which are
beginning to be identified, compromise the anterior insula structure
and function. Because no brain region operates in isolation, it will
also be relevant to fully characterize the brain network of which the
insula is a part.
Beyond the domain of BPD, the innovative approach used in this study of
a personality disorder can also be applied to other severe mental
illnesses in which social dysfunction is a prominent source of
disability, such as schizophrenia or autism. Such an advance should be
warmly welcomed by patients, their therapists and researchers.
http://www.sciam.com/article.cfm?id=borderline-personality-disorder&page=2
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