In normal members of the population, theta waves are associated with drowsy, meditative or sleeping states. Yet in psychopaths they occur during normal waking states - even, sometimes, during states of increased arousal...
"Language, for psycopaths, is only word deep. There's no emotional contouring behind it. A psycopath may say something like "I love you", but in reality it means about as much to him as if he said "I'll have a cup of coffee"... This is one of the reasons psychopaths remain so cool, calm and collected under conditions of extreme danger, and why they are so reward-driven and take risks. Their brains, quite literally, are less "switched on" than the rest of ours."

The observation that modern-day humans are pathologically risk averse does not, needless to day, mean that this has always been the case. In fact, it might even be argued that those of us today who are clinically risk averse - those of us, for instance, who suffer from chronic anxiety - simply have too much of a good thing. During the time of our ancestors the existence of individuals who were hypervigilant to threat may well, evolutionary biologists suggest, have been decisive in the fight against predators - and from this point of view, anxiety would undoubtedly have served as a considerable adaptive advantage. The more sensitive you were to rustlings in the undergrowth the more likely you'd have been to have kept yourself, your family and your extended group members alive. Even today, anxious individuals are better that the rest of us at detecting the presence of threat: slip an angry face in among a display of happy or neutral faces on a computer screen, and anxious people are far faster at picking it out than those who are non-anxious - not a bad ability to fall back on should you happen to find yourself alone at night and wandering around an unfamiliar neighbourhood. Being anxious can sometimes be useful.

In a survey which has so far tested 14,000 volunteers, Konrath has found that college students' self-reported empathy levels (as measured by the Interpersonal Reactivity Index) have actually been in steady decline over the previous three decades - since the inauguration of the scale, in fact, back in 1979. And that a particularly pronounced slump has, it turns out, been observed over the past ten years.
"College kids today are about 40 per cent lower in empathy than their counterparts of twenty or thirty years ago," Konrath reports. More worrying still, according to Jean Twenge, professor of psychology at San Diego State University, is that, during this same period, students' self-reported narcissism levels have, in contrast, gone in the other direction. They've shot through the roof.

"People think [psychopaths] are just callous and without fear," he says. "But there is definitely something more going on. When emotions are their primary focus, we've seen that psychopathic individuals show a normal [emotional] response. But when focused on something else, they become insensitive to emotions entirely."

As one hugely successful young attorney told me on the balcony of his penthouse apartment overlooking the Thames: "Deep inside me there's a serial killer lurking somewhere. But I keep him entertained with cocaine, Formula One, booty calls and coruscating cross-examination."
Ever so slowly, I moved away from the edge.
This aerial encounter with the young lawyer (he later ran me back to my hotel down river in his speedboat) goes some way towards illustrating a theory I have about psychopaths: that one of the reasons we're so fascinated by them is because we're fascinated by illusions, by things that appear, on the surface, to be normal, yet that on closer examination turn out to be anything but.