Antisocial Personality Disorder (APD) is characterized by irresponsibility, dishonesty, impulsiveness, bad temper, lack of emotional depth and conscience, and lifelong antisocial behaviour. Researchers of the University of Southern California have studied 21 men who were all diagnosed with the disorder, all of them having committed serious violent crimes. Using brain-imaging techniques, researchers discovered that the antisocial men had an 11%–14% reduction in the volume of nerve cells in the prefrontal cortex compared to normal males. This region seems to house the mental gear that enables most of us to gather moral awareness and to exercise discipline.

Previous research has shown that violent criminals have poor functioning in that region, located just behind the eyes. The new findings demonstrate that a physical abnormality resulting in Antisocial Personality Disorder may underlie the poor functioning in these violent antisocial men and that society may have to rethink how it regards violent crime, punishment, and the scope of free will.