Men who are most prone to rage and violence have significant deficiencies in a brain region that enables most people to learn moral sensibilities and exercise self-restraint, researchers at the University of Southern California have shown.
The study joins a growing body of findings that may force society to rethink how it regards violent crime, blame, punishment and the scope of free will.
"Our previous research had shown that convicted murderers -- really violent offenders -- have poorer functioning in the brain's prefrontal cortex," said USC psychopathologist Adrian Raine. In a study published in the Feb. 1 issue of the Archives of General Psychiatry, Raine and colleagues demonstrate that a physical abnormality may underlie the poor functioning in these violent, antisocial men.
Neurologists have long been aware of a strong link between damage to the prefrontal cortex and the acquisition of antisocial, psychopathic-like personality changes. Raine's study bolsters this link by taking people with lifelong antisocial tendencies and showing that they have prefrontal damage.
The prefrontal cortex is the brain's foremost outer portion, located right behind the eyes. Vital in the orchestration of emotion, arousal and attention, it seems to house the mental machinery that enables people to restrain themselves from acting on all of their impulses. The prefrontal cortex is thought to be central to a child's ability to learn to feel remorse, conscience and social sensitivity.
The 21 men studied were all diagnosed with Antisocial Personality Disorder (APD), which is characterized by irresponsibility, deceitfulness, impulsiveness, irritability, lack of emotional depth, lack of remorse, and life-long antisocial behavior. All of them had psychopathic personalities and had committed serious, violent crimes.
Using brain-imaging techniques, the researchers measured tissue volume in the prefrontal cortex. They found that the antisocial men had an 11 to 14 percent reduction in the volume of nerve cells in the prefrontal cortex compared to normal males -- a deficit of about two teaspoons' worth.
Raine suggests three reasons why prefrontal deficits may cause antisocial personality:
First, the region appears to be critical for self-restraint and deliberate foresight. "One thing we know about antisocials is that they do not think ahead," said Raine.
Second, it's crucial for learning conditioned responses -- essential, for example, to a child's linking the thought of a misdeed with anxiety over punishment. "Unconscious mental-emotional associations such as these lie at the core of what we call conscience," Raine said.
Third, if prefrontal deficits underlie the APD group's low levels of autonomic arousal, these people may unconsciously be trying to compensate through stimulation-seeking. "For some kids," said Raine, "one way of getting an arousal-jag is by robbing stores or beating people up."
Reduced prefrontal volume and lower autonomic responses predicted APD with an accuracy of 76.9 percent. In fact, Raine explained, the prefrontal and autonomic deficits were just as good at predicting whether a subject has APD as were the 10 "psychosocial risk factors" -- including poverty, parental criminality, and physical and sexual abuse -- also considered in the study. Combined, biological and social factors were 88.5 percent accurate in predicting APD.
This new study is the first structural brain-imaging study of any antisocial group, Raine said, and is significant because the subjects come from the general community rather than prisons, and because the study was controlled for some important factors, such as substance abuse and mental health problems unrelated to APD, that could have been directly associated with the brain deficit.
Clinical, functional and structural findings like Raine's are adding up to a persuasive case that antisocials, growing up from birth or early childhood with prefrontal deficits, have the deck stacked weightily against them.
"We are talking about a predisposition to antisocial behavior," Raine stressed. "Some people who have prefrontal deficits do not become antisocial, and some antisocial individuals do not have prefrontal deficits. It's important to make clear that biology is not destiny."
Even so, Raine's findings raise important ethical questions about culpability and free will. "To what extent," he asked, "should we take disordered brain functioning into account as part of the reason for certain types of crime? Assuming these people are not responsible for their own brain damage, should we hold them fully responsible for their criminal acts?"
At present, there is no way to repair large-scale brain damage or deficits. Still, Raine said, society could move to address the problem of biologically based violence. "Let's not forget the physical and sexual abuse or the poverty. That's very important. But I think one reason we have failed to provide effective treatments and interventions is that we have ignored the biological side of the equation.
"We need to focus resources on that small group of kids, the 5 percent, who will commit 50 percent of the crime and violence later in life," Raine continued. "Tackling imprisoned adults is almost a waste of time. Tackling kids when they're juvenile delinquents is far too late. We have to get to these kids much earlier in life, when the brain is more plastic."
Raine suggested a number of interventions that could be applied. Cognitive and behavioral therapy and drug therapy have potential. Biofeedback -- training children or adults to control their own arousal levels -- could be a useful tool. And children could be channeled into safe activities that might satisfy their natural stimulation-seeking and aggressive proclivities, steering them clear of the antisocial, criminal lifestyle into which they are otherwise likely to fall.
"Studies in England show that army bomb-disposal experts have low resting heart rates," Raine said. "That's very interesting, because it makes me wonder whether biological predispositions to antisocial behavior could be adaptive, too. Society needs fearless people, after all, people who might contribute to society as bomb-disposal experts, firefighters and test pilots if they could be identified and helped in time."
Raine, a professor of psychology in the USC College of Letters, Arts and Sciences, is first author of the journal article and author of a book titled "The Psychopathology of Crime: Criminal Behavior as a Clinical Disorder."
Co-authors of the journal article are Todd Lencz, Hillside Hospital, North Shore-Long Island Jewish Health System; Susan Bihrle and Lori LaCasse, department of psychology, USC College of Letters, Arts and Sciences; and Patrick M. Colletti, department of radiology, USC Keck School of Medicine .
This study was supported by grants to the first author from the National Institute of Mental Health and the Wacker Foundation.
Materials provided by University Of Southern California. Note: Content may be edited for style and length.
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