A very readable summary about recent views on Psychopaths over here on Jonah Lerner's blog. 
The popular view of psychopaths is that they are monsters who could also be serial killers. That is a myth. The majority of psychopaths are not criminals. They are people you know at work or in your social circle. They may even be the people you are now living with. They are people with emotional deficits who may not look that way at first sight.
Having met at least 3 psychopaths, I was struck by their charm. The ones I knew were amusing, handsome, likeable people. They were also interesting, in the sense that they had arresting opinions, different from the usual run. Later on I discovered that they were also self-centred manipulators who seduced other people using charm and sheer plausibility. They also left a lot of damage behind: fraud, rape, lies, damaged lives.
In Reverse Therapy, psychopaths are interesting because they are an extreme example of what happens when the thinking centres are divorced from emotion, Headmind from Bodymind.
Specifically, a region in the decision-making centres, the orbito-medial cortex just above the eye-brows, is unable to register sadness, fear or disgust (although it can react to anger and pleasure). Nor can it pick up the corresponding emotions in other people for the simple reason that empathy is based on the ability of the orbito-medial cortex to interpret the emotions you have taken over from others in order to assess their emotional state. That information is useful for the rest of us for the simple reason that we use empathy and emotion in order to decide how we can best help other people. The psychopath does not do that. Instead, she is more interested in outcomes.
In the film Malice, Nicole Kidman was coached how to play a psychopath as follows:
'You're walking down the street and come across an accident at the corner. A young child has been struck by a car and is lying in a pool of blood. You walk up to the accident site, look briefly at the child, and then focus on the grief-stricken mother. After a few minutes of careful scrutiny, you walk back to your apartment, go into the bathroom, stand in front of the mirror, and practice mimicking the facial expressions and body language of the mother.
If you want to spot a psychopath, or, in fact, any kind of phony, then pay close attention to what they do rather than what they say. And, remember, that charm can be deadly.
The desert is squeezed in the tube train next to you.
The desert is squeezed in the heart of your brother
T. S. Eliot.
