­­­When most of us think of killers like Ted Bundy or John Wayne Gacy, we imagine people who feel compelled to harm other huma­n beings, who enjoy causing fear and who feel no remorse for their actions. And for the most part, these characterizations are entirely correct. Serial killers (and many other types of violent criminals) are typically considered to be psychopaths with aggressive and anti-social characteristics. But not all psychopaths are violent -- some are "merely" manipulative, dishonest and incapable of experiencing deep emotions, and they may blend in with society with relative ease. A CEO who cheats his employees out of their pensions and then walks off without a tinge of regret may be a psychopath. Psychopaths, violent or non-violent, have no "moral compass," no conscience. They do not experience feelings of guilt for the crimes or betrayals they commit. A recent study of the brains of psychopaths, published in the British Journal of Psychiatry, may shed some light on what's going on -- or not going on -- in these people's heads.

For years, researchers and psychiatrists have understood that psychopaths respond differently to external stimuli, and they have theorized that this abnormal response is rooted in the brain. The idea is that psychopaths process information differently than non-psychopaths, and numerous scientific studies using functional MRI (fMRI) to visualize brain activity have backed this up. In 2003, a study presented at a conference in Britain showed that when "normal" people lie, there is increased activity in the frontal lobe that suggests the experience of guilt and discomfort; but when psychopaths lie, there is no increased brain activity. An earlier study found that when psychopaths viewed emotionally charged words like "rape" or "murder," the changes in their brain activity were completely different from the changes that occurred when non-psychopaths saw those words. The increased brain activity in the psychopaths wasn't even in the limbic system, which is where language processing occurs.

In 2006, a group of London-based scientists published the results of a study that may offer additional information on the biological basis for psychopathy. It appears that psychopaths may experience the signs of fear in other people in a way that is not comparable to the way most of us experience it. In fact, they may not really experience it at all.

©AP Photo/Mark Foley
Ted Bundy, executed in January 1989 for the savage murders of at least 16 women

­The study set out to test the idea that psychopaths don't experience empathy for other people's distress -- can't understand, sense or appropriately react to it -- because they don't grasp the signs of that distress. In particular, this study tested the responses of nine "normal" people and six criminal psychopaths to typical facial and vocal signs of fear and sadness. All of the subjects were hooked up fMRI equipment that measured their neurological responses to the stimuli. In this context, "response" typically means increased bloodflow and/or increased firing of neurons, the carriers of brain signals.

The researchers showed both groups of subjects two different sets of images: one of joyful faces and neutral faces, and one of fearful faces and neutral faces. The neutral faces established a baseline for brain activity.

When the non-psychopathic subjects saw a happy face, the fusiform and extrastriate regions of the brain -- the areas primarily responsible for processing images of facial expressions -- showed increased activity compared to their response to a neutral face. The psychopathic brains also showed increased activity in response to the happy faces, although less of an increase than in the non-psychopathic group. However, whereas the non-psychopathic subjects showed a similar increase in brain activity in response to the distressed faces, the psychopathic subjects did not. In fact, when the psychopaths were shown sad or fearful faces, their brain scans actually showed less neural activity than when they were shown neutral faces.

The researchers concluded that in psychopaths, the neural pathways that are supposed to process signs of human distress are either non-functional or work completely differently than those pathways work in the general population. This could explain, at least in part, why psychopaths do not identify with the emotional distress of their victims. The findings of the study may be helpful in understanding how psychopathy works at the neurological level, but in a BBC News article, psychopathy researcher Dr. Nicola Gray of Cardiff University explains, "it is still a long way to finding out what to do about that."

Related HowStuffWorks Article­s
* How Serial Killers Work
* How Jack the Ripper Worked
* How Police Interrogations Work
* How Crime-scene Investigation Works

More Great Li­nks

* BBC News: What makes a psychopath?
* CourtTV Crime Library: Psychopathy
* RxPG News: Criminal Psychopaths showed reduced activation in brain when processing emotional facial expressions


* "Cri­minal Psychopaths showed reduced activation in brain when processing emotional facial expressions." RxPG News. Dec. 1, 2006.
* "Psychopaths' brains 'different'." BBC News. Dec. 4, 2006.
* Ramsland, Katherine. "All About Dr. Robert Hare: Expert on the Psychopath." CourtTV Crime Library.
* Ryan, Caroline. "What makes a psychopath?­" BBC News. Sept. 18, 2003.