Where in the depths of the human brain does violent behavior have its inception? Scientists are not sure, but reduced prefrontal gray matter and decreases in total brain volume and temporal-lobe volume have been linked with violent behavior in some people with antisocial personality disorder. In addition, poor orbitofrontal functioning, an abnormally large putamen, and abnormally small amygdalae and hippocampi have been linked with violent behavior in some schizophrenia patients.
And now aberrations in cortical thickness have been linked with violent behavior in both types of subjects. The findings come from Arthur Toga, Ph.D., director of the Laboratory of Neuro Imaging at the University of California at Los Angeles, and his coworkers. Their findings were published in the September American Journal of Psychiatry.
Toga and his coworkers used magnetic resonance imaging to compare regional differences in cortical thickness in four groups of subjects—14 individuals with antisocial personality disorder and a history of violence, 12 individuals with schizophrenia and a history of violence, 15 individuals with schizophrenia but no history of violence, and 15 healthy nonviolent comparison subjects. All 56 subjects were right-handed and closely matched on demographic variables.
The scientists found that cortical thinning in the medial prefrontal cortex differentiated the violent antisocial group from the other three groups and that cortical thinning in the sensory motor cortex differentiated the violent antisocial group and the violent schizophrenia group from the two nonviolent subject groups.
Moreover, the findings add to the evidence that while violent subjects with antisocial personalities and violent subjects with schizophrenia share some common structural brain abnormalities, differences do exist.
How might a thinning of the prefrontal cortex set the stage for violence? It might impair judgment, emotion, self-monitoring, and impulsivity, the scientists proposed in their study report. And how might a thinning of the sensory motor cortex prep the brain for violence? By compromising movement in some way, the scientists speculated. That is, while they found no differences in motor speed between the violent groups and the nonviolent ones, they did find deficits in eye-hand coordination in the former.
The study was funded by the National Institutes of Health and the Stanley Medical Research Institute in the United States, and the Zito Trust, Community Fund, and Wellcome Trust in the United Kingdom.
