http://www.psych.ubc.ca/babble/archive/2001/may01/story9.htm

Among researchers who are starting to explore this area, there are two
main theories of psychopathy. One, championed by Adrian Raine of the
University of Southern California in Los Angeles and supported by the
work of Antonio Damasio of the University of Iowa, gives a starring
role to a brain region called the orbitofrontal cortex (see diagram,
below). This is part of an area of the brain, known as the prefrontal
cortex, involved in conscious decision-making. Damasio has shown, for
example, that patients who have suffered damage in this area early in life
have severe social behavioural problems and can be very aggressive9.


Last year, Raine's team published an MRI study of 21 men diagnosed
as having APD, who admitted--under guarantee of confidentiality--to
having committed violent crimes12. Compared with normal volunteers,
these men had shrunken prefrontal cortices--reduced in volume by up
to 14%. The results grabbed the headlines, but their signifiicance for
true psychopathy remains unclear. Again, the volunteers had not been
rated using the PCL-R, and shrunken prefrontal cortices are also
associated with substance abuse--so the finding could merely indicate
an associa- tion between drug-taking and APD.