Using fMRI imaging, a team of researchers looked at the brain signaling of 50 men: 12 violent offenders—all people with antisocial personality disorder and psychopathy who had been convicted of murder, rape, attempted murder or grievous bodily harm—20 violent offenders with antisocial personality disorder but not psychopathy, and 18 non-offenders.

While their brains were being scanned, the men completed an image matching test that measured their ability to change their behavior and choices based on feedback they were getting from the game. The psychopathic men had a much harder time with changing their behavior, and they took significantly longer to adapt when the game changed its rules.

Scans of the psychopaths’ brains looked different from both non-psychopathic criminals and non-offenders, showing noticeable abnormalities in their white and gray matter—both of which are involved with connecting brain regions. The abnormalities were observed in areas of the brain where emotions like guilt, embarrassment and moral reasoning are processed. Some of those abnormalities were linked to a lack of empathy.