James Fallon was almost 60 when he learnt the truth about himself. And it was by accident. In 2005, the US neuroscientist was poring through brain scans for research when he stumbled upon the signs of that infamous rarity in human nature: a psychopath.

They weren’t the first he’d spotted – he’d just finished a study where incarcerated killers were brought in for scans, shackled and under the watch of “a SWAT team on the university roof”. But this psychopathic brain had turned up in the control group of a separate study he was running into Alzheimer’s and schizophrenia. He and his own family were among the healthy volunteers imaged. All the scans were anonymous, so Fallon assumed the psychopath got mixed in by mistake (or perhaps as a practical joke). “When I looked at the brain activity, I knew this was a bad case. I thought this person can’t be just walking around in the world, so I got the lab to check the name.”

When it came back, Fallon made them run it again. He laughed, but it wasn’t a joke, and it wasn’t a mistake. The name on the scan was his.

Fallon, who has devoted his career to life-saving neurological research, was later diagnosed as a high-functioning psychopath. He also learned that he was descended from three lines of “murderers and scoundrels”, including distant cousin Lizzie Borden, who was tried for murdering her father and stepmother with an axe in 1892 (although acquitted). “This sounds like a movie, I know,” he laughs.

The discovery would make Fallon rethink the importance of nurture as opposed to nature. Biologically, his brain had all the markers of a dangerous psychopath. “But I’d never wanted to hurt anyone,” he says. Though he’d always been a risk-taker, driving fast cars and motorbikes in his youth, extreme skiing, he’d never run afoul of the law. “I had no need to, I had a great childhood, surrounded by this sea of love in a big Irish Sicilian family who kept an eye on me, kept me busy. So I got lucky. I turned out like this instead of those bad guys I’d studied. Mind you, I still can’t let even my own granddaughter win at Scrabble.”

So what makes someone a psychopath? How are they different from a narcissist or a sociopath? And can it be treated?

Who are psychopaths?

When you think of a psychopath, you’re probably not thinking of someone like Fallon: upbeat and quick to laughter. Perhaps the chilling stare of Norman Bates is what comes to mind first – that fictional killer haunting Alfred Hitchcock’s 1959 thriller Psycho. Or the vacant eyes of American Psycho’s Patrick Bateman, portrayed in the movie by Christian Bale, who asserts, between his own violent rampages through Wall Street, “I have all the characteristics of a human being – blood, flesh, skin, hair – but not a single, clear, identifiable emotion, except for greed and disgust.”

“The media love the word ‘psycho’,” says forensic psychiatrist Dr Danny Sullivan who assesses offenders for court, works at Melbourne’s high-security mental health hospital, Thomas Embling, and has met his fair share of psychopaths. “But psychopathy does not mean crazy.”

Bates killed while in the grip of a psychosis. Bateman too, though more the picture of cold remorseless psychopathy in his designer suits, was also experiencing delusions. Psychopathy, by contrast, Sullivan says, tends to be stable over time. “It’s not a mental illness that you’ve developed one day. This is kind of hardwired into your personality.”

While those who are mentally unwell are more likely to be the target of violence than to carry it out, psychopaths are much more likely to harm those around them.

The term (which literally means “suffering soul”) gets bandied around a lot. People diagnose their in-law or their boss. But, in clinical terms, Sullivan says, “psychopathy is [used] to explain a particular cluster of personality traits” in someone. “Often that’s inexplicably cruel behaviour, what we see as outside the range of decent human behaviour. In some ways, it’s really a moral diagnosis.”

People can have psychopathic traits without quite making the cut-off for clinical psychopath, Sullivan adds. That’s determined by psychiatric assessment. Fallon himself sits right on the borderline.

While those who are mentally unwell are more likely to be the target of violence than to carry it out, psychopaths are much more likely to harm those around them. A high percentage of violent offenders are psychopaths and a high number of psychopaths are violent offenders.

But that doesn’t mean all psychopaths are violent – or serial killers, although there is certainly some crossover. Ted Bundy, for example, is often called the perfect psychopath – charming, manipulative, without remorse and prone to risk-taking. He used his boy-next-door looks and elaborate con stories to lure his victims, later admitting to raping and murdering at least 30 women during the 1970s after long years of denial, two dramatic escapes from custody and even a heavily publicised turn at defending himself in court. But sadism, where someone derives pleasure from hurting others as Bundy did, is a separate condition to psychopathy.

“So you get [non-violent] guys like me too, more in the middle who [go unnoticed],” says Fallon, who has consulted on TV and films depicting psychopaths including Criminal Minds.

Still, the words of Patrick Bateman are not far off the mark. Psychopaths are probably best recognised by a lack of empathy. At Cambridge, leading autism expert Simon Baron-Cohen (cousin of the actor and filmmaker Sacha) argues that, while people on the autism spectrum might struggle to understand other people’s emotions, psychopaths have the opposite problem – they are brilliant manipulators and mimics, able to use people’s feelings and desires against them, but they do not feel that emotion for others, generally treating people as expendable. One of those emotions they don’t feel the way most of us do is fear, and so they are more likely to take risks and act impulsively.

Some studies look to detect psychopaths by showing people upsetting images and measuring their physiological and neural responses. As Sullivan explains, “Most people, if they see a cat in pain, will start to show signs of distress themselves. It’s why we try to do the right thing most of the time. We don’t like harming. But a psychopath can’t feel that empathy in the same way, so if you’re oblivious to that, you could harm people with impunity.”

Many of the psychopaths at the more extreme end of the spectrum are not particularly successful, Sullivan adds. They end up in prison. Their charm and deception are flimsy: you can see through them. “Of course, most of the studies of psychopathy have focused on this criminal cohort. But there might be a second class of successful psychopaths sitting in super-yachts around the world, climbing the corporate ladder.”

Some research estimates as many as one in five corporate bosses are psychopaths – about the same prevalence as in prisons. This statistic is generally thought to be overblown, but Sullivan and Fallon both agree that at least 1 per cent of the world’s population are psychopaths, with likely higher numbers exhibiting some psychopathic traits.

And most psychopaths are men. The ratio may be as high as 20 male psychopaths for every female, leading some to wonder if a key driver of the disorder lies in our hormones. Still, other studies suggest that the expression of psychopathy in women may look different too – notably less aggressive – and so slip under the radar more often.

How do you detect a psychopath? What if you’re a psychopath?

The first psychopath test I try is 26 questions long, scoring how strongly I relate to statements such as “People who are stupid enough to get ripped off usually deserve it” (strongly disagree) and “I don’t plan very far in advance” (yeah OK, agree). I score very low on “lack of empathy and remorse” (phew, not a psychopath then), although higher than average on “boldness” in each of the five online tests I churn through in the name of “research”.

Fallon smiles. He recalls living in Africa and going out among the wild animals – “too far out, apparently, like dangerously close so anyone who came with me would freak out, but I have no desire to die. I just know how to push things right to the limit.”

OK, perhaps I’m not that bold. Of course, you need a psychiatrist to diagnose you with psychopathy, not Google. People will over or underinflate their answers depending on how they want to perceive themselves. But a strong sign you’re not a psychopath? Worrying you might be a psychopath. “We don’t care,” Fallon says. “I didn’t care. It was a surprise, that’s all.”

The most common test used in diagnosis today was first developed in the ’70s by Robert Hare, a Canadian forensic psychologist, who became fascinated with unravelling the mystery of psychopathy after being confronted (and charmed) by one among the inmates he treated in prison. Hare helped that particular inmate, known as Ray, secure a plum prison job in its car repair shop. But when Hare had his own car serviced there to celebrate his last day of work, he soon discovered that the brakes had been deliberately rigged to fail on a time delay (he only barely made it to safety).

Ray had many of the traits of a psychopath that now feature on Hare’s Psychopathy Checklist including superficial charm, pathological lying, sexual promiscuity, a parasitic lifestyle and juvenile delinquency and criminality. Fallon shares some but not all. “But before I was diagnosed, when I saw the scan and started asking people who knew me, they all said, ‘Oh yeah, you definitely do psychopathic things.’”

Something Fallon says he doesn’t enjoy doing is lying. Yet full-blown psychopaths do it routinely, Sullivan says. “Everyone manipulates people during a job interview, for example. You’re trying to put some spin or gloss on things. Well, psychopaths are doing that all the time. There’s an astonishing amount of deception going on. You might never get the true picture of who that person is.”

“Everyone manipulates people during a job interview, for example. You’re trying to put some spin or gloss on things. Well, psychopaths are doing that all the time.”

So what gave Fallon’s brain away as psychopathic?

Coincidentally, his own research into psychopathic killers about two decades ago was among the first work into the neurological structure of psychopathy. When he looked at their scans compared to the general population, he saw a pattern. And he saw it again when he looked at his own – an entire section of the brain, the social and emotional processing centre known as the limbic system was dark. “It’s almost turned off in psychopaths,” he says.

Studies since have reached similar conclusions, finding less grey matter than normal in this region, suggesting psychopaths lack “the neural equipment” to feel empathy for others.

“We have what we call cognitive empathy, rather than emotional,” Fallon explains. “It’s not automatic, we have to think about it.”

The amygdala that mediates high emotion such as fear and anxiety also functions less (an inversion of anxiety disorders where it is often overactive).

How are they different from sociopaths and narcissists?

Clinically, the terms sociopath and psychopath can be interchangeable, Sullivan says, both falling under “antisocial personality disorder”. But, more broadly, a psychopath is understood as someone born with the condition. A sociopath is made. In some cases, biological markers can be found in both – a child’s brain may not develop properly if exposed to abuse early on in life, for example, as was well documented in the sad case of Romanian orphans deprived of human contact growing up who later showed cognitive impairment. There are even cases of acquired psychopathy, Sullivan says, where brain damage alters someone’s personality.

Fallon sees it this way: “If you have the genetics that make you susceptible to [psychopathy] and then you’re abused or traumatised, you’re ripe to become a full-blown psychopath. Whereas if you don’t have the genes, but you’re abused early on, you’re more likely to be a sociopath. They’re two different animals. Well, they might be sub-species, but there’s a difference.”

“With psychopaths, we don’t even really think about it. It’s almost play. We just do what we want. We win.”

Often sociopaths are less stable (and less successful) than psychopaths, Fallon adds. They might be driven to violence or callous behaviour by ideology or revenge, a sense they’ve been wronged, rather than the cold dispassionate logic of a psychopath. “So someone spurned by a redhead who parted her head in the middle at 13 starts killing redheads who part their hair in the middle,” he says. “But [to them] there’s a reason behind it. With psychopaths, we don’t even really think about it. It’s almost play. We just do what we want. We win.”

That’s why you rarely see a full-blown psychopath on screen, he says, with the character of the assassin in No Country For Old Men an exception. “There’s nothing to root for. Even Dexter had to love his sister. Even Jaws the shark had a vendetta of sorts. It was personal. Well, it’s never personal.”

There are overlaps between psychopathy and other conditions too, namely the other two sides of the “dark triad” – narcissism and Machiavellianism. Psychopaths tend to have overinflated egos, focused on themselves and their needs without consideration of others, as narcissists do, Sullivan says. “So narcissistic personality disorder has a lot of overlap with psychopathy, but also with things like solipsism [a condition where someone believes they are the only person who really exists].”

Likewise, people who score high for Machiavellianism (named for the ruthless philosophies of the Italian renaissance diplomat Niccolo Machiavelli) tend to also score high for psychopathy – they are cunning and ruthless. But they often have better impulse control, and their capacity for empathy or morality may be higher than a clinical psychopath, and so they can be thought of as more immoral (breaking moral codes) than without them altogether (amoral). “Just like the sociopath is the real sinner, they know what they’re doing is wrong,” Fallon says.

Are there advantages to psychopathy? Are they smarter?

Sullivan tends to meet psychopaths in prison, with his guard up. Some are the “distempered”, aggressive type rather than the charismatic mould we see most often on screen. “But the charming ones are more dangerous in a way because they draw you in,” Fallon says. “You get in the car with them.”

And they can be very “likeable”, Sullivan agrees. “Sometimes you won’t realise you’ve been hoodwinked until later. But they will often tell you they’re more intelligent than they really are.”

While functional psychopaths such as Fallon can fly under the radar, Sullivan says most full-blown psychopaths get caught. “At that end of the spectrum, their lives are so disorganised,” adds Fallon. “It’s almost impossible for them to function well. That’s a bit of a myth, a Dr Lecter evil genius type getting away with everything.”

He acknowledges his own psychopathy has helped him succeed. “[As a psychopath], you’re competitive, you get things done, you know how to take chances.”

“Probably the best depiction of a psychopath on screen was Hal, the spaceship’s sentient AI in 2001: A Space Odyssey.”

Still, while he has a high IQ, he says there doesn’t appear to be a clear link between psychopathy and intelligence. Rather, he thinks psychopaths appear smart because they are not slowed down by the usual social considerations. It’s almost as if the reptilian brain that houses our most basic needs can bypass that longer route through the limbic system and go straight to the problem-solving centre of the frontal lobe, he says. “You’re not distracted by emotions. Those things that make you a machine make you seem smarter. Really, probably the best depiction of a psychopath on screen was Hal, the spaceship’s sentient AI in 2001: A Space Odyssey.”

Some argue that the profit-driven, high-stress culture of corporate life is fuelling a rise in psychopathic traits by rewarding them. Some professions, such as surgery, can even induce a kind of “stress immunity”, at times potentially accentuating psychopathic traits that make it easier to do things like pick up a scalpel and slice into someone to save their life.

Fallon has studied autocrats such as Russian President Vladimir Putin (“a likely functional psychopath, a clever one”) and says fearless dominance is still considered an attractive trait in a leader – that ability to make snap decisions with authority, whether they are right or not.

Sullivan agrees that those able to disregard the emotions of others may seem like a more effective leader. “They’re willing to exploit people for profit, to say crush unions or tolerate the deaths of workers, despoil the environment, or manipulate to improve their share price. You can look at a range of business leaders and argue it could be an adaptive trait for certain aspects of capitalism.”

In fact, some experts argue that psychopathy needs to exist, at small levels, to help the entire human species thrive. Fallon understands the theory, noting, “What’s terrible for the clan can be good for the species”. “Psychopaths appear brave, they do things others won’t, [they’ll] go over the mountain, spread their genes. And they also tend to be very lucky because they don’t make decisions out of fear, so they win more.”

In an evolutionary sense then, “thank God for psychopaths,” Fallon laughs. “Or else maybe we wouldn’t exist.” Too many psychopaths, though, and it all falls apart.

Is there any treatment?

Of course, psychopathy at an individual level can have devastating consequences. They may never have healthy relationships, hold down a job, and the people around them can get hurt.

While psychologists do keep their eyes open to early warning signs of psychopathy, including harming people and animals, Sullivan says children are not diagnosed. “Can you imagine picking a kid out in grade three and saying, ‘You’re at risk of psychopathy, we’re going to put you into an intensive program.’ That kind of labelling can set someone on a bad trajectory in the first place.”

All psychiatry must be wary of being too deterministic about criminal behaviour, he says. And there is rarely a definitive box to explain anyone. But for psychopathy at the extreme end of the spectrum, Sullivan says, “we can’t change their core personality. There’s no medication or psychiatry for that so we manage their behaviour instead”, refocusing their attention towards positive or creative activities.

That often means teaching a psychopath that treating people well and following social or moral codes will lead to more benefit for them, especially in a prison or mental health facility, where he says many psychopaths are detained. “If you’re good, you’ll get more freedom, more luxuries.”

While some might imagine psychopaths ruling the prison yard, Sullivan says they tend not to do well in groups. “They disrupt, they manipulate”.

“I don’t like to see people in pain, but I manipulated them, I left them in the lurch, I was careless.”

Still, there could be some pharmaceutical treatments yet on the horizon. Sullivan points to ideas to trial the “bonding” hormone oxytocin in psychopaths to see if it fosters increased empathy. “They’re already looking at it experimentally in people with autism to see if it can help foster [understanding of emotions] but some wonder if it will help psychopaths feel emotions too,” he says.

Fallon himself is working with a start-up to study how to better regulate serotonin in the brain, in order to treat anxiety and depression – which could have a flow-on effect for psychopathy. So too could promising research into the use of psychedelic drugs to treat mental health disorders.

In the meantime, Fallon has been carefully moderating his own behaviour for the past decade. When he was diagnosed, he realised he was having “a bad effect on some people” around him. “I don’t like to see people in pain, but I manipulated them, I left them in the lurch, I was careless.” “My father used to say I’m such a good con man but I don’t actually think about it. If I was entertaining people with stories at a party, say, my wife says it’s like I was trying to bring them into my world, to own them.”

So he started his own experiment. For each interaction he had, especially with his family, he tried not to be selfish. “And I watched my friends with their kids, really good guys. I noticed they often did things no one knew about, little things like cleaning the dishes or pouring a glass of wine for their wife first. I tried to be like that.”

It was exhausting work – Fallon says he started sleeping hours more each night. But he’s kept it up ever since. “I don’t know what could have happened [in my life] but I know what did. I know how I was raised, when to pull back.” And his family know “not to take [him] too seriously”.

But to Fallon personally, the label “psychopath” means nothing. “In my own skin, I feel great. Life is a candy shop. And that pisses some people off. They say, ‘You’re so happy’ and I say, ‘Well, we’re alive. We can do anything.’ And they say, ‘No, you can do anything. I can’t do that.’ And I say ... well, I don’t know what to say to that.”