Adrian Raine, D.Phil., chair of criminology at the University of
Pennsylvania, has a passion. It is peering into the brains of antisocial
people to see whether their brains differ from those of people who are not
He is finding that such a difference does in fact exist.
For instance, in 2000, he and his coworkers reported that the prefrontal
cortex was significantly smaller in violent, antisocial men than in controls
(Psychiatric News, March 3, 2000). In 2005, he and his colleagues
reported that pathological liars had more white matter in the prefrontal
cortex than normal control subjects (Psychiatric News, November 18,
2005). And now he and his colleagues reported, in the September Archives
of General Psychiatry, that the amygdalae of psychopathic individuals are
significantly smaller than those of nonpsychopathic
The amygdala regions of the brain are known to process emotions and
especially to play a role in fear. So Raine and his colleagues suspected that
the amygdalae of psychopaths might differ from those of nonpsychopaths, and
they launched a study to test the hypothesis.
Individuals who sought work through temporary employment agencies were
recruited for the initial phase of the study. They were screened with the Hare
Psychopathy Checklist-Revised. The instrument assesses people for factors such
as superficial charm, cunning and manipulation, pathological lying,
impulsivity, irresponsibility, callousness, lack of remorse, and other
psychopathic traits. A score of 23 or higher is used to define
The researchers found 27 individuals who had a score of 23 or higher on the
checklist and enrolled them in the second phase of their study. They then
found 32 individuals who scored very low on the checklist (scores of 5 to 14)
and who matched the 27 psychopathic subjects on age, gender, and ethnicity.
These 32 individuals were enrolled as controls in the second phase of the
During the second phase, the left amygdala and the right amygdala of each
of the 59 subjects were measured with structural magnetic resonance imaging.
Both the left and right amygdalae in the psychopathic group were found to be
significantly smaller than those in the control group. These results held firm
even when two possibly confounding factors—socioeconomic status and
substance/alcohol dependence—were considered.
Thus, "amygdala structural abnormalities are a key element in the
neurobiological bases of psychopathy," the researchers concluded.
The researchers suggested that the possession of amygdala abnormalities
might "contribute to [the] emotional and behavioral symptoms of
psychopathy." One reason why they believe this might be the case is that
rats and monkeys with amygdala damage have been found to display a lack of
fear, as psychopathic individuals are likely to do. Another reason may be that
some patients who have experienced amygdala damage as a result of disease have
been found to have difficulty responding to facial expressions. Psychopathic
individuals may have the same problem.
It's possible, of course, that the opposite is the case—psychopathy
leads to abnormalities in amygdala volume—or that some other factors
lead to both psychopathy and amygdala abnormalities.
The study was funded by the National Institutes of Health.
An abstract of "Localization of Deformations Within the
Amygdala in Individuals With Psychopathy" is posted at<http://archpsyc.ama-assn.org/cgi/content/abstract/66/9/986>.▪