"I didn't know what made people want to be friends. I didn't know what made people attractive to one another. I didn't know what underlay social interactions."

"I don't feel guilty for anything. I feel sorry for people who feel ."

“I'm as cold a motherfucker as you've ever put your fucking eyes on. I don't give a shit about those people.”

These creepy Ted Bundy quotes patently summarize the main traits of a psychopath: A callous, exploitive individual with blunted emotions, impulsive inclinations and an inability to feel guilt or remorse.

The causes of psychopathy remain a mystery. We don’t even have a satisfactory answer to the question of whether psychopathy is a product of Mother Nature or a feature of upbringing. One of the best sources of information about whether traits are a result or nature of nurture comes from the Minnesota Study of Twins Reared Apart. The Minnesota Twin Study is a project originally led by Minnesota Professor of Psychology Thomas Joseph Bouchard, Jr. The Minnesota twin study has shown that psychopathy is 60 percent heritable. This percentage indicates that traits are due more to than to upbringing. Recent genetic studies of twins indicate that identical may not be as genetically similar as hitherto assumed. Though only a couple of hundred mutations take place during early fetal development, the mutations likely multiply over the years, leading to vast genetic differences. This leaves open the possibility that psychopathic traits are largely genetically determined.

If psychopathy is genetically determined, one should expect some abnormality in the brain, the immediate source of psychopathic traits. A possible candidate for this abnormality has recently been identified in a study at University of Wisconsin, Madison. Brain scans revealed that psychopathy in criminals was associated with decreased connectivity between the amygdala, a subcortical structure of the brain that processes negative stimuli, and the ventromedial prefrontal cortex (vmPFC), a cortical region in the front of the brain that interprets the response from the amygdala. When the connectivity between these two regions is low, processing of negative stimuli in the amygdala does not translate into any strongly felt negative emotions. This fits well into the picture we have of psychopaths. They do not feel nervous or embarrassed when they are caught doing something bad. They do not feel sad when other people suffer. Though they feel physical pain, they are not themselves in a position to suffer from emotions hurts.

The Wisconsin, Madison study shows a correlation between criminal psychopathy and brain abnormality. As this brain abnormality in the majority of cases of psychopathic criminals is not abruptly acquired, there is good reason to think that it's grounded in the psychopath's DNA.

There are, however, some limitations of this study. The study measured criminal psychopaths. But not all psychopaths are criminals. Most psychopaths are manipulative, aggressive and impulsive but these features far from always lead to criminal activity. It remains to be seen whether non-criminal psychopaths, like their criminal counterparts, have reduced activity between the amygdala and the vmPFC. Another limitation of the study is that it doesn’t show that reduced activity between the amygdala and vmPFC is an abnormality specifically linked to psychopathy rather than to a range of mental conditions that have been associated with serious , including and extreme sexual fetises.

Though the Wisconsin study sheds some light on what may bring about the traits of psychopathy, psychopathy remains puzzling. We don't know the reason behind the reduced connectivity in the emotional system. It could be caused by a dysfunction of neurotransmitters, for example, by a disturbance to the main excitatory neurotransmitter glutamate. Alternatively, it could be a degenerative disease that leads to a reduction of the brain’s white matter, which is responsible for connectivity among neurons. The answer to what causes reduced connectivity in the brain’s emotional system would help answer some of the bigger questions about psychopaths, for example, the question of whether disorder is partially due to social (or other environmental) factors or is primarily genetically based.

Social factors have some (even if only small) role to play in generating psychopathy. But after many years of investigating the minds of psychopaths, researchers have been unable to find any factors that could contribute to the development of psychopathic traits. Early abuse or neglect often leads to posttraumatic disorder or phobias (e. ., in terms of making commitments). But disorders are typically associated with either greater connectivity between the amygdala and the vmPFC or a dysfunction of vmPFC that makes it unable to modulate negative information from the amygdala. We cannot exclude that childhood abuse or neglect may be a factor in making psychopaths commit crimes, but it's not a likely contributing factor to psychopathy itself. Furthermore, though serial killers like Charles Manson were abused and neglected as children, the list of serial killers with a normal childhood is long. Famous serial killers such as Ted Bundy, Jeff Dahmer and Dennis Rader grew up in healthy households with supportive family members.

Elsa Ermer and Kent Kiehl of the University of New Mexico, Albuquerque, discovered that psychopaths have difficulties following rules based on moral sensibility, despite fully understanding the rules. The blunted emotions of psychopaths appear to play a role in preventing them from following rules. But this is possibly correctable. We know that people with have difficulties picking up on social cues or do the right things in social contexts. But higher functioning autists can normally learn to make the right kinds of signals in social situations. For example, they can learn to make eye contact, back-channel during conversation and express an interest in other people. Sometimes this requires years of training with a therapist or medical professional. They have to learn to do what others learn by interacting with family members and peers. If people with high-functioning , an inheritable disease, can learn social cues, then presumably some psychopaths can learn to follow moral rules by going through extensive training.

One social factor in turning a genetically disposed individual into a psychopath, then, may be a negative one: They have not been given special training in following rules. Perhaps given their dull affect, one could experiment with training programs that increase negative emotion processing artificially and then teach them to associate these heightened negative emotions with morally bad actions. Certain hallucigenics, such as psilocybin, might be an effective tool.

It is worth noting here that a large number of the most gruesome crimes were committed by psychotics, not psychopaths. and psychopathy are different kinds of mental disorders. Psychosis is a complete loss of one's sense of reality. Psychopathy is a disorder, much like . are potentially more permanent and less curable than psychotic diseases.

Psychotics and psychopaths can have traits in common, such as blunted emotions, but they differ in terms of whether they are in touch with reality. Psychopaths are calculating and manipulative but they do not suffer from or delusions. They do not hear the voices of strangers in their heads or hold elaborate false theories about the world. Serial killer Coral Eugene Watts strangled several women because he saw evil in their eyes. Belle Sorenson Gunness slaughtered her husbands because she believed men were evil. Ed Gein mutilated, skinned and gutted his graveyard goodies and his only live victim because he wanted to be a woman and believed he needed body parts for a change (or maybe to make a replica of his mother). Richard Trenton Chase drank and bathed in his victims' blood. He believed he had to do this to prevent Nazis from turning his blood into powder with a poison they had hidden beneath his soap dish.

One hypothesis about psychotic diseases, such as and , is that the glutamate system is dysregulated. Overstimulation may lead to phases, delusions and hallucinations. Lack of stimulation could lead to blunted or negative affect. The overstimulation and lack of stimulation may happen at the same time at different receptor sites. The mechanism underlying psychopathy and psychosis may thus overlap with respect to the blunted or negative affect.