Kent Kiehl was walking briskly towards the airport exit, eager to get home, when a security guard grabbed his arm. "Would you please come with me, sir?" he said. Kiehl complied, and he did his best to stay calm while security officers searched his belongings. Then, they asked him if there was anything he wanted to confess.

Kiehl is a neuroscientist at the Mind Research Network and the University of New Mexico in Albuquerque, and he's devoted his career to studying what's different about the brains of psychopaths – people whose lack of compassion, empathy, and remorse has a tendency to get them into trouble with the law. On the plane, Kiehl had been typing up notes from an interview he'd done with a psychopath in Illinois who'd been convicted of murdering two women and raping and killing a 10-year old girl. The woman sitting next to him thought he was typing out a confession.

Kiehl recounts the story in a new book about his research, The Psychopath Whisperer. He has been interviewing psychopaths for more than 20 years, and the book is filled with stories of these colorful (and occasionally off-color) encounters. (Actually, The Psychopath Listener would have been a more accurate, if less grabby title.) More recently he's acquired a mobile MRI scanner and permission to scan the brains of New Mexico state prison inmates. So far he's scanned about 3,000 violent offenders, including 500 psychopaths.

He talked with WIRED about what's different in the brains of psychopaths and why he views psychopathy as a preventable mental disorder.

WIRED: How do real life psychopaths differ from ones we see on TV or in movies?

Kent Kiehl: One of the biggest differences is that psychopaths are way more common than people believe. About one in 150 people will meet the stringent clinical criteria for the disorder. That means hundreds of thousands of them are out and about in the population. The majority of them don't commit violent crimes, but they lead this sort of disorganized, nomadic life, and they tend to eventually end up in some sort of trouble. Hollywood hasn't done a good job of portraying the average psychopath. For the most part, they've taken the extreme view, with the Hannibal Lecters and more sensationalized people like that. It's actually far more common and banal.

WIRED: People also tend to confuse psychopathy and psychosis – what's the difference?

Kiehl: Right. With psychopathy the main features are lack of empathy, guilt, and remorse – and impulsivity. Psychosis is a fragmentation of the mind where you have hallucinations and delusions. It's a very different disorder. You almost never find someone who has psychotic delusions and even moderate levels of psychopathic traits.

WIRED: In the book you write that in two decades you've only come across a handful of people who scored 40 out of 40 on the psychopathy checklist (30 is commonly used as the psychopath cutoff. Regular folks tend to score around 4 or 5). What is it like to talk to a perfect psychopath?

Kiehl: They are so fundamentally different. You leave the room knowing that you've just met someone who is extremely different, even different from other psychopaths. They are absolutely and completely free from conscience. They have this unbelievably flat affect that's really palpable when you look in their eyes.

Kiehl stands at the entrance of his mobile MRI scanner. Photo: courtesy of Kent Kiehl

WIRED: It sounds like the sort of thing that would stay with you for a while…

Kiehl: Yeah. One of my favorites I call Shock Richie because he did some things that most of us would not even think were possible – the types of crimes he committed, the things he would do to the bodies afterwards. He would do things purely for shock value. When he walked into the maximum security prison on his first day he took off all his clothes and walked around completely naked out in the rain. All the other inmates were wondering what the hell was going on. I interviewed him later that day and he told me he does stuff like that to make sure people understand he's capable of anything.

WIRED: What's going through your mind when you're sitting in the room with someone like that?

Kiehl: I'm just fascinated.

WIRED: Aren't you ever worried about getting your ass kicked?

Kiehl: Well, more than just getting my ass kicked. I worked with a guy who admitted to me that he'd committed several murders on the outside and would commit more if people would ask. He had a team of confederates. I got a phone call a few days later from the head corrections officer at the prison where I was working at the time and he said "Kent, we're taking you into protective custody. One of the inmates thinks you ratted him out and is talking about having you killed." So my roommate and I went into protective custody for a couple days. It turned out that one of his confederates had snitched on him. Once that information got back to him, I went back to work as if nothing had happened. But there was a time there when I was worried about someone taking me out.

WIRED: Is it hard to spend so much time around people who've done really awful things?

Kiehl: I'm pretty comfortable with it. I've only met maybe 2 or 3 people in my career who after talking to them, I realized I just don't need to know anything else about them. They've done such bad things and the way they dealt with it… I got to my limit.

WIRED: Why do you see psychopathy as a mental disorder, not just an extreme personality type?

Kiehl: I consider it a mental health problem because it's associated with impairments at home, at work, with family, with friends. It leads to hospitalization or incarceration. It comes with all these other problems you associate with mental illness. The one thing that differentiates psychopaths is they don't appear distressed by the fact that their life is a disaster. They lack insight into how their behavior affects other people.

WIRED: What is known at this point about what's different about their brains?

Kiehl: We've found that psychopaths have 5 to 10 percent reduced gray matter density in and around the limbic regions [a network deep in the brain that's important for emotional processing]. We've also found – and a group in Germany has published a similar finding – that the tissue that connects the limbic system to the frontal lobes is disrupted. There have also been lots of studies published showing reduced responsivity in those circuits during emotional processing and moral decision making.

Kiehl's research has identified brain regions that are less dense in psychopaths. Image: Kent Kiehl

WIRED: You write in the book about your testimony for the defense in the death penalty hearing for Brian Dugan, the psychopathic serial killer who almost got you in trouble with the TSA. Is the neuroscience really ready for use in individual cases?

Kiehl: It depends on the context. The evidence is pretty convincing that their brains are different, the question is whether it's mitigating or not. As an attorney, I think you'd only want to bring up an issue like psychopathy if the only question before the jury was life or death. That was the context in the Dugan case. All he's going to be doing is going back to his cell for the next 15-20 years [the jury apparently first returned a life sentence, then changed it to a death sentence, which was converted back to life in prison when Illinois abolished the death penalty in 2011].

But I don't think it makes sense at all to use psychopathy as a mitigating factor in a juvenile first time offender or that type of context. There's a potential double-edged sword. There's a possibility a prosecutor could say, well if his brain is different, doesn't that mean there's a higher risk he'll reoffend, and how would you change it?

WIRED: Can psychopaths change?

Kiehl: I'm so encouraged by the pioneering work that's occurring at places like the Mendota Juvenile Treatment Center in Wisconsin, where people are taking high risk youths [who show signs of developing psychopathic traits] and treating them with various intensive programs to try to reduce the odds that they'll reoffend.

The treatments that seem to be making a big difference emphasize positive reinforcement rather than punishment. Yes, they're incarcerated at the time and that's their punishment for the crimes they've done, but the facilities instead of only punishing them when they do something bad actually reward them when they do something good. If they interact positively with staff they're given a small reward, like maybe a video game in their cell for the weekend. Similarly, with this segment of the population, if you use positive reinforcement they're much more likely to do what you want them to do.

__WIRED: __Does it really make sense to devote the resources for intensive therapy to such a small minority?

Kiehl: If you look at just the published literature on the Mendota Juvenile Treatment Center, for every $10,000 the state of Wisconsin has invested on that program, it returned over $70,000 in reduced incarceration and criminal justice costs in the next four years. Boys that go through the treatment stop accumulating infractions that lengthen their sentence. When they get out, they stay out longer and they commit less violent crime, which is the most expensive kind of crime from a societal perspective.

__WIRED: __If we already have interventions that work, why do we need all the brain research?

Kiehl: The current programs aren’t perfect. They reduce violent recidivism by 50 percent. But 10 to 15 percent of kids still reoffended violently, despite the best psychological treatment. What the brain science might do is help inform the cognitive treatment process so maybe you could determine that the easy to treat kids might be ready for release after six months, but these other kids need a full year or more of treatment. You might be able to use the neuroscience to improve the decision making. That’s the sort of thing we’re hoping to do.