He refers to it as "that moment Gandalf knocks on your door," summoning him on a great mission. He told his wife of many decades, who wasn't surprised. Then he just let this knowledge lie for a couple years, like so many of us do when it comes to disturbing things like lingering health concerns, or recently purchased exercise equipment.

But others had taken notice of Fallon's probable diagnosis long before he did -- be they family, or the top psychiatrists in Norway. See, Fallon was asked to give a talk on bipolar disorder at the University of Oslo in 2010, and for ethical reasons, he used his own brain scans for the PowerPoint presentation. Some of the country's top psychiatric minds invited him to a friendly, hours-long chat after -- nothing fancy, understand; just a "thanks for participating! We think you're probably a borderline psychopath" kind of affair.

"That's the first time I took it seriously," Fallon says. "They didn't know me, but they knew my biological and psychological data."

jamirae/iStock Usually inappropriate vacation pics accidentally slipping in are the worst thing of yours co-workers see in your PowerPoint presentation.

Fallon had stumbled across what Dr. Kent Kiehl already knew too well. Kiehl has spent years lugging a mobile MRI machine to prisons to analyze the brains of high-rating psychopaths, and he knew that the scans of a psychopath show much lower than normal activity in the areas of the brain responsible for impulse control and "emotional responsiveness," among other things. Kiehl published some of the first studies showing that brain scans can predict antisocial behavior. If this sounds a little too Minority Report for you, keep in mind that it's much more accurate than a lot of the risk equations we use today -- take, for example, parole boards -- to predict recidivism:

"We have a whole field of psychology that tries to assess by proxy things that are happening in your head -- your IQ, your age, all these variables ... Those are all measures that are trying to assess what's happening inside the head, whereas what neuroscience is doing -- we're simply being able to say, well let me quantify the brain data directly, rather than by proxy."

mstroz/iStock Or by phrenology.

So what's it like to be a psychopath?

Fallon puts it this way:

"I don't get anxious about things, and if I've done something wrong, I'm challenged by somebody catching me." He also says his pain threshold is very high, consistent with psychopathy. "I drove my dentist crazy, root canals with no anesthesia ... I think it's just a kick. The way I feed that particular monkey is being around danger."

cw-design030/iStock That's right. His dentist was like, "That's a little too psychopathic, even for me."

And if you're wondering how a neuroscientist like Fallon wouldn't know he had such a notorious diagnosis, well, he argues his experience is pretty textbook ...

In other words, consistency is key. You may have committed a few mind-bogglingly horrible, unforgivable-in-the-eyes-of-society-or-your-exes transgressions, but there are a number of other mental illnesses or personality disorders that could account for that.

But there is a range for how much of a psychopath you are. Fallon says that he, himself, rates "mostly mid-20s, from 20 to 28" on the Hare checklist. That would make him a borderline psychopath in the U.S. (although a "true" psychopath for research purposes), and a total psychopath in the U.K.

Adrian Pingstone According to the British, 90 percent of the world suffers from "poor impulse control."

Although Kiehl was not talking about Fallon in particular, he points out that someone who falls short of a full-blown psychopathy diagnosis, but has a higher-than-average score -- say 20 or beyond -- is not someone you want to date: "They're not going to have all of the same problems because it does run on a gradient, but they are someone who is not likely to lead to happiness for those around them all the time."

Fallon's personal inventory doesn't exactly undermine this idea: "I do things that are really quite dangerous with people -- with my young kids, my brothers, and I push it right to the limit," Fallon says. "To me, I'm a thrill-seeker. Physically and socially, (I do) some dangerous things." For example: While working at the University of Nairobi hospital, he took his son fishing at Mount Kenya ... disregarding all the signs warning of impending lion attacks in the area. Later, a guy came into the hospital bleeding out of his nose, suffering from the Marburg virus, which has shocking similarities to Ebola. Rather than avoiding, well, the plague, Fallon says, "I found out where he had stayed ... he went into the Kitum Cave, where the old elephants, the old matriarchs, bring the young ones to dig out the caves to get iodine and all the minerals. My brother came (to visit), and I said 'I'm going to give him a thrill here.' I knew nobody was going to the place."

Because of rebels shooting in that area, naturally.

Richard Preston And the elephant ghosts.

"I knew there were a lot of animals, and no tourists. So we went in there, and I didn't tell my brother anything. I took him into the caves and I said, 'Don't touch the ground.' The virus was living in the batshit, and that's where this guy got it from. I went in, there were bats all over, it was wild. We stayed overnight at this camp, where this guy had stayed. All night, animals -- leopards, hyenas -- were all around us, because it was a clearing. I said, 'We gotta keep this fire going, it's very important.' It was like a scene from Quest For Fire, with us brandishing these logs, screaming at these animals to keep them back."

He still talks about it like it was a grand adventure. His brother only found out about the cave when 1995's Outbreak hit theaters. "He said, 'You son of a bitch, you knew it all along, but you still brought me there.'"

Mnolf/Wiki Commons So, psychopathy really is closely related to batshit insanity.

And there is a kind of junior version of Hare's Psychopath Checklist, used for those aged 12 to 18. And it continues: "Essentially, the younger you get, the harder it is to access what's happening in the brain, but there have been people trying to assess it as early as four, five, six."

While a postdoc, Fallon worked with a leading expert who claimed to be able to distinguish psychopathy in two- and three-year-olds. The guy wouldn't go on record saying so, fearing the public outcry that would inevitably distract him from his work, "but he told me that he could see it. He could follow them until they're in their 20s. And they all had been abused, or some problem like that, so that's a key thing."

This is where Fallon's life gets decidedly Sliding Doors.

Scenario A: The fucked-up, full-blown psychopath lifestyle of self-serving violence, broken relationships, sporadic employment ...

OR

Scenario B: Life as a scientist and an academic, happily married, his relationships with his children intact.

What differentiates them?

THEPALMER/iStock One is way better at hiding it?

"I had all the biological markers, but I was never abused as a kid," Fallon said. "Look, you can have the biology, but it's not a death sentence. If you treat kids well, don't abandon them, they're not going to clinically have these pernicious (habits/traits)."

He also credits the women in his life. "Even friends growing up -- not just as adults -- said, 'If it wasn't for your girlfriend, (then) wife, you'd definitely be in jail.' She had a very stabilizing influence on me. My mother, my aunts -- the whole matriarchy kept me in line."

Kiehl notes that every adult psychopath he worked with was "different from normal children from a very early age. Their prison files are typically replete with stories from siblings, parents, teachers, and other guardians about how as a child the psychopath was emotionally disengaged from other siblings, got in trouble more frequently, engaged in more severe antisocial behaviors, and started using alcohol and drugs and having sex at a younger age than other children."

Much of that holds up for Fallon. "My mother knew there was something wrong. She was worried about me. After I wrote the book, she told me she was really concerned about me."

TanyaRu/iStock "Leaders of multiple religions declared you a troubled child! Also, you never call."

She had always noticed his "'tendencies toward being a bad boy.' She just kept me really busy, all the time. I was always involved in sports." Often the more violent, the better. "Plus skiing and swimming. Any other time I was involved in acting. And she knew the teachers, and she as a teacher said 'Keep this kid busy.' When I am not busy life gets dark around me. I'm just busy all the time. It's a good thing for the people around me."

While his mother's savvy over-scheduling mostly kept him out of trouble, Fallon's lagging limbic system still had some influence. "I just had this tendency, even when I was being a good boy: I always try to get groups of people to do things that was against their conscience. It was never to hurt anybody. It was for fun, it was goofy."

But Kiehl has seen a lot of hope in young, burgeoning psychopaths! He tells us ...

One of her patients, for example, doesn't realize he isn't empathetic:

"One of the things he was telling me was he feels really protective toward women and children, and that always gets him in trouble. He says, 'Say I see a woman jogging in the park and I see some shady characters hanging around. I'd want to go up to her, and warn her about them ... if it was my mom, I'd want someone to do that for her.' I said, 'But do you think your mom would want that?' And he got a really confused look on his face. I said, 'You know, you've got to think about it from that lady's perspective: She doesn't know you from those strangers or anybody, and you're just approaching her. She might feel afraid.' It was like a brand new idea to him."

KatarzynaBialasiewicz/iStock Even psychopaths are receptive to the cutting "your mom!" rebuttal.

Kiehl believes even the psychopath brain is capable of change, but it's best to start early. He is a huge supporter of a program at the Mendota Juvenile Treatment Center in Wisconsin, which has had an unprecedented 50 percent success rate in reducing violent outcomes among boys who score high on the Youth Psychotherapy Checklist.

As Kiehl writes: "The (Mendota) model was founded on the belief that prison deterrence and prisoners' defiant responses can become a vicious cycle. As they cycle repeats itself, prisoners give up more and more investment in convention, and their lives become 'compressed' as the use of punitive and restrictive sanctions increases. Eventually ... the only response left in their behavioral repertoire is violence." Fallon agrees: "What Kent's saying, if you try negative reinforcement on (a psychopath), the brain interprets it as abuse. Since they do not appreciate what bad behavior is, they think it's completely unfair. To them it's not immoral or anything."

The program takes a minimum of about 10 to 12 months to have any effect, but you can't argue with the results, or the rosy economic benefits -- it's all been peer-reviewed. "That's the only program in the world that has done that," Kiehl says, and this gives him hope for adult psychopaths, too. "(Kids are) potentially more malleable than adults, but that doesn't mean I don't believe the program would work with an adult, it just might take two or three times as long. Once you get entrenched in your behaviors and your attitudes, changing those things can take as long a time as long as it took you to get ingrained in them."

That's one battle. Another?

The Talented Mr. Ripley fits more cleanly into the "psychopath" category -- he seduces, forges false identities, and kills for either personal gain or simple convenience -- but he would likely have a secondary diagnosis of "psychosis" (a different thing!) according to this exhaustive, whimsical study of silver-screen psychopaths, which argues that Wall Street's Gordon Gekko is a mere manipulative psychopath, while Patrick Bateman is indeed the full-blown American psychopath.

Lionsgate Films Anyone who cares that much about fonts knows no human empathy.

Moving on to a more nuanced cocktail conversation: It's popular to use "sociopath" as a point of reference for shitty people. Cut it out. According to both Fallon and Kiehl, it's passe.

"'Sociopathy' was a term coined in the behaviorist era of psychology, when it was believed every human was a blank slate at birth," Kiehl explains. "So 'socio' means social forces, 'pathy' means pathology -- created by environment. We know now that psychopaths are not solely made by their environment, so that term ('sociopathy') is not used in academic circles anymore." Likewise, maybe consider tossing out your copy of The Psychopath Test. Kiehl called Jon Ronson's popular book "a work of fiction" and points out that it's "the only book that the Society for the Scientific Study of Psychopathy publicly opposed."

Riverhead Books Also opposed by the Society for Cover Design for other reasons.

"I just have never seen someone who scores in the top percentile of the Hare test be very successful," Kiehl says. "The way they go about life, and go about manipulating, and the way they go about lying, basically -- they're lazy. They don't follow through with anything. They're not going to be a good employee."

Fallon explains that he was able to become professionally successful, despite his diagnosis. "Somebody who scores very high, over 30, that's a dangerous person. For people like me, who have high scores on maybe half of them -- I scored very high -- you'd say you're a borderline. For me, I have all of the pro-social psychopathic traits ... I'm not quite a categorical psychopath. And if I was a psychopath, I wouldn't able to be quite successful. A 35-scoring psychopath tends not to have a successful life at all. They tend to get disordered and they get caught at some point."

Fallon theorizes that genetics worked in his favor, which is a bit ironic, because, well: "We have four lines of killer in our family. That's too many." Lizzy Borden is a distant cousin; his great-and-then-some grandfather, Thomas Cornell, brutally murdered his elderly mother in the late 17th century.

"We have direct fathers and grandfathers, grandmothers, really badasses, murderers. But the other parts of the family, we have a couple nuns, ministers -- they're either very holy or (murderous). I have a first cousin, he's gone the other way, he's getting his doctorate after years of being a teacher. He's going through the spiritual history of my family, instead of genetics, (with the theory) that they passed down a sense of holiness."

via Wiki Commons Dude, you just called insane murderers "badasses." Your psychopathy's showing again.

In his family, Fallon thinks that the very gray area, which Kiehl has long studied, can be "turned on all the time, or off all the time."

As for true, full-blown psychopaths? Well ...

And goes on to tell us: "One of the classic definitions is that (psychopaths) are willing to engage in a wide variety of different crimes. You'll see psychopathic -- even more so than non-psychopathic -- inmates who will experiment in just about any different type of criminal activity. Whatever opportunity plays by. They usually don't develop an expertise ... the types of crimes they commit are wide-ranging."

That said, he has found psychopaths are more likely to commit homicides.

"We've published studies on the types of crime psychopaths commit, and the types of aggression profiles you see. They're more likely to obviously abuse close relatives or spouses than others ... There are a lot of other types of more aggressive violent crimes (that) are perpetrated by psychopaths, but the vast majority of crimes psychopaths commit are non-violent crimes."

Lionsgate Films Even Bateman did ten shady acquisitions for every execution.

In his book, Kiehl writes about a particular subject, "Gordon," whose future plans included "leveraging some of his residual bank-robbery proceeds to start a motorcycle dealership." His rap sheet included not only robbery, but nearly stabbing a girlfriend's alleged lover to death. His cellmate, "Grant," was in for murdering his two accomplices in a robbery. Grant was quick to add that he'd also dabbled in arson, credit-card fraud, some assorted B&E's, and a string of other murders of convenience. Grant was, of course, a serial killer.

More optimistically, Kiehl says:

"That's where neuroscience, I think, is going to help. What it does is tells us which regions of the brain are immature that are contributing toward that (unwise) decision. And then you can develop a program or treatment that tries to exercise or work on that system. Or maybe there's medicine that helps them work on that system."

To get a deeper understanding of mental health, check out You've Met One Today: 5 Creepy True Facts About Psychopaths and 5 Things Everyone Gets Wrong About Mental Illness.

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