Psychopath: the very word conjures up the image of a deranged killer. Yet the Hollywood portrayal of psychopaths has only served to conceal a disturbing truth: that many of us share our workplace or even our home with cunning psychopaths adept at masking their malevolence. They may never have committed a crime or resorted to violence, yet they share the same cold, manipulative and chillingly self-centred mindset of a serial killer.
Such corrosive personalities have been with us for millennia. According to the American psychiatrist Dr Hervey Cleckley, who pioneered research into the subject in the 1940s, the Athenian statesman and general Alcibiades shows all the classic traits, from childhood delinquency and dishonesty to a complete lack of scruples or remorse. Latter-day candidates for the label of "socialised" psychopath range from Josef Stalin and Saddam Hussein to the author Ian Fleming - perhaps not coincidentally, the creator of the famously ruthless fictional hero James Bond.
Given their malign impact on those around them, from workplace bullying to marital violence and even murder, psychopaths have long been a focus of psychiatric research. To date the results have largely left unresolved the enigma of this destructive personality disorder. But now researchers are uncovering important new clues about its causes.
Psychiatrists are clear that, whatever else they might be, psychopaths are not insane. Indeed, they appear to have an all too effective grasp of reality, being able to manipulate those around them to fit their self-centred grand plan.
Attempts to explain the underlying cause have drawn on everything from the results of brain scanners and electroencephalograms to questionnaires and genetic analysis. Some researchers have focused on the mental "hardware" of psychopaths, looking for signs of brain damage, while others have looked for faulty "software".
Other studies have shown that while they might not be psychotic, psychopaths don't view other people and relationships as they should.
A classic test devised by Dr Robert Hare, an emeritus professor at the University of British Columbia and the doyen of psychopath research, involves putting together words with similar meanings. Given three words like "warm", "loving" and "cold", psychopaths will tend to put together "warm" and "cold", while the rest of us will link "warm" and "loving". It seems that psychopaths just don't understand that an emotive phrase like "loving" might have anything to do with the physical notion of "warmth".
The notorious lack of genuine warmth and empathy shown by psychopaths suggests that they lack what psychiatrists call "Theory of Mind", or ToM.
Put simply, this is an ability to understand the thoughts of other people, and to put oneself in their shoes. Such an ability is clearly crucial for forming and maintaining relationships, and integrating properly with society. Those lacking such an ability notoriously struggle to form normal human relationships.
Given their harmful interactions with their fellow human beings, psychopaths might seem to have some flaw with their own Theory of Mind. Yet one of their most disturbing characteristics is their grasp of what others are thinking and willingness to exploit this for their own ends. That suggests their ToM is perfectly intact.
A way through this apparent paradox is now being explored by researchers, however. They suspect that a person's ToM is actually made up of two distinct elements, one of which is devoted to understanding other people's beliefs and motivations, the other allowing people to gauge the feelings and emotions of others. If so, it may be that psychopaths lack the empathetic element of ToM, making them utterly indifferent to other people's feelings.
Psychiatrists already know of a class of patients with damage to a part of the brain called the orbitofrontal cortex (OFC) who also have problems with empathy. Could it be that the root cause of psychopaths is a similar "hardware" problem caused by damage to their OFC?
To investigate this possibility, Professor Simone Shamay-Tsoory and her colleagues at the University of Haifa, Israel, gave a group of 14 prison inmates diagnosed as psychopaths a series of tests designed to test both aspects of their ToM. The results were then compared with those from patients with damage to the OFC brain region, and to healthy patients.
The results, published recently in the research journal Cortex, showed that psychopaths performed in a strikingly similar way to patients with damage to the OFC region of the brain.
Has the riddle of the psychopath finally been unravelled? Given the complexity of the condition, it's unlikely that damage to just one part of the brain can be the sole explanation.
But the key unanswered question is whether this new research might one day lead to a cure for this most destructive of personality disorders. One thing is for sure, however: if a treatment does emerge, we shouldn't expect psychopaths to see any reason to undergo it. In their eyes, it's not them that have a problem - it's us.
Robert Matthews is Visiting Reader in Science at Aston University, Birmingham, England