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How should society deal with psychopaths? What do we do with violent offenders such as rapists and serial killers? Adrian Raine, a psychologist who moved from his job at a high-security prison to the University of Southern California, believes that for a small minority, violence is not a matter of choice. Their biology prevents them from following the same moral code as the rest of us. So is it right to judge them by the same standards as the rest of society? Alison Motluk caught up with the man who thinks such offenders should be spared the death penalty and their brain scans allowed as mitigating evidence in murder trials.

What is a psychopath like?

They are individuals lacking conscience. They have no sense of guilt. They are lacking in remorse. They don’t experience emotions in the way we do. Supposedly they are superficially charming. They have a grandiose sense of self-worth, they are egocentric, they are impulsive. They move from person to person, manipulating, conning, preying on people. About 25 per cent of prison inmates really fit the full clinical picture.

So are there shades of psychopathy, even in normal people?

I tend to view it as a continuum. I believe that there are people out there-functioning people-who have some degree of psychopathy but not at a clinical level. Some of the traits of psychopathy could be useful. In normal times we put those people in prison, but in times of war we put them on the front line. There are some famous politicians who’ve shown degrees of psychopathic-like behaviour, including presidents of the United States. To get a strong, successful, charismatic leader who will stop at nothing-maybe that requires a certain degree of psychopathy.

You’ve looked at a number of biological measures for psychopathy. What are the strongest associations you’ve found?

Low physiological arousal is one of the strongest predispositions to later antisocial behaviour-things like low resting heart rate, low sweat rate, slow-wave brain activity. We did a study in England on schoolboys, just unselected schoolboys. We measured their physiological arousal at age 15, then followed them for nine years till they were 24. We found that the schoolboys with low physiological arousal were the boys who grew up to become criminal offenders.

Why is arousal important at all in violent criminals?

One theory is stimulation-seeking. If you have low levels of arousal, you seek out stimulation to increase your levels to normal. For some kids that’s burgling a house, robbing a store, beating someone up.

Of course, not everyone does that. We know from some studies in England that bomb disposal experts have very low heart rates. You can take two people, both with low physiological arousal-one grows up to become a violent criminal, who may take a life, whereas the other grows up to become a bomb disposal expert and saves a life.

You’ve looked at criminals’ brains too. What’s different about a violent offender’s brain?

We did a brain imaging study specifically looking at murderers. So here we had 41 murderers, who’d all killed somebody in California. Then we had 41 matched controls-normal people who hadn’t committed any crime of violence. We used a technique called PET, positron emission tomography. We were looking at the brain’s function by assessing its glucose metabolism. Cells use glucose as their fuel. The more glucose a region is using, the more active that brain area is. We gave them all a task where numbers ranging from 0 to 9 are flashed on a screen. What the subjects have to do is press a button every time they see the figure 0. Numbers are flashed on the screen once every second for 32 minutes, and you have to keep watching second by second to spot the number 0. It’s a very dull, very boring task, but vigilance is one of the functions of the prefrontal cortex and we know from previous research that this activates that region.

As expected, we got good brain functioning in the normals. But the murderers showed a distinct lack of functioning in the prefrontal region of the brain, the part of the brain that fits right above your eyes and lies behind your forehead.

Why should a faulty prefrontal cortex cause violent behaviour?

This part of the brain is involved in regulating and controlling behaviour. It’s the part of the brain that makes us think twice before we do anything. If it’s damaged, you don’t stop and think, you’re more likely to act out your aggressive impulses. The prefrontal cortex is a bit like the emergency brake on a car. When the car gets out of control, we pull on the emergency brake. But for the violent offender, there is no emergency brake.

Maybe they don’t use the emergency brake much, so it’s stopped working?

You’re saying, maybe the part of the brain is structurally there, it’s just not being used. To look at that question, we did another study. We measured the volume of prefrontal cortex in the brains of violent antisocial individuals. I obtained 21 individuals who met a psychiatric diagnosis of what’s called “antisocial personality disorder”. This is really serious repetitive antisocial behaviour starting at an early age. Some of these people were responsible for homicides.

We scanned them and found that the group with antisocial personality disorder who were violent criminal offenders had an 11 per cent reduction in the amount of grey matter in the prefrontal cortex. The grey matter are the nerve cells. The white matter are the white nerve fibres that connect the nerve cells, like telephone wire. So in our free-range offenders we found a structural deficit in the very same part of the brain that we found to be functioning poorly in the murderers.

What do you think could be the cause of the brain abnormality?

Birth complications create brain damage, sometimes subtle, sometimes overt. These are things like forceps delivery, breach birth or lack of oxygen to the fetus. We did a study where we measured birth complications in 4269 live male births in Copenhagen, Denmark. When the babies were one year of age, we interviewed their mothers and measured “maternal rejection”: Mom didn’t want the child, or he had been institutionalised for at least four months.

We followed up these 4000 kids until age 18 and found out which ones became violent criminal offenders. The answer is: it’s the kids with both the birth complications and the maternal rejection. It’s when you have both the biological and the social factors coming together that you are especially likely to have violent criminals offending.

Yet if a person had a shrunken prefrontal cortex, low levels of arousal and so on but had had a perfect upbringing, you could still predict with some accuracy that they’d offend?

Exactly. These brain deficits were quite independent of the social deficits. Interesting that you mention that, because in the study we did on the murderers, we actually divided them into those from good homes and those from bad homes. And we found that it’s the murderers from the good homes who are especially likely to have the poor frontal functioning. If you’re violent and you come from a good home, what’s causing the violence? It’s more likely to be a biological brain deficit.

Have you ever testified in court on the side of a murderer?

There was one time when I did testify. It was an individual who had a head injury, and who we did believe had a number of biological and social predispositions to later impulsive violent behaviour. He had committed a double homicide. But the jury still found him fully responsible and guilty.

Did you believe he wasn’t really guilty?

I believe he was guilty to some extent. To some degree he had control over his behaviour. But I also believe that this individual had suffered both social and biological deficits early in life which, let’s say, predisposed him to becoming violent.

We’re not responsible for what we inherit, but surely we’re responsible for what we do with it?

I think what you’re saying is that despite all this, they can still choose. There’s nothing forcing them to go out and kill. You could say it’s a bit like alcoholism. Alcoholics know they have a problem, their biological and genetic predisposition makes them more likely to drink. So they have the responsibility to seek help, to do something to reduce their risk to society. You could say the same is true of these violent criminal offenders-they know they have these risk factors and they ought to do something about it. That’s fine, but the part of the brain that’s responsible for self-reflection and insight is the prefrontal cortex. And it’s damaged. It’s a double whammy.

Is this what you mean when you ask in one of your books, “Is crime a disorder?”

Indeed, yes. What I am arguing is that, as with schizophrenia or depression or alcoholism, we know that there are social and biological factors that come together fairly early in life to create mental disorders. And I think the same is true of crime and violence. There are people who commit violent crimes who have none of the predispositions. I do believe in freedom of will. I do believe that people can of their own free will choose an evil path in life. I actually believe in the death penalty. If those people kill others they in turn should be killed.

But you don’t believe in the death penalty for these natural born killers?

I don’t believe there are natural born killers. But there are natural biological factors that increase the odds of a person becoming a violent offender. And I think it’s very different for these people. I think if we can establish that there are biological and social predispositions that occurred early in life and were beyond their control, and if we can establish-as we are beginning to do-that these factors play a causal role in shaping violent criminal behaviour, then I think we have to think twice about whether we execute these people.

So what should we do with psychopaths?

I think there’s very little that can be done. We have to protect society: we clearly can’t let these people out. But should we punish them as harshly as we do? What we have to try and do is prevent them from getting to that position. We have to tackle the early factors that create conduct disorder and antisocial behaviour in children. If you do this you won’t get adult psychopathy. Behavioural, drug and cognitive intervention have all been successful. The idea is that antisocial personality disorder is an outgrowth of this trend that begins early in life.

Do you think that persistent violent offenders should have prefrontal cortex scans?

Any information about a person’s biological and social risk factors for violence is relevant to a court case.

Should scan results-together with other relevant information, for example, birth complications and upbringing-be taken into account when sentence is passed?

If somebody has been physically and sexually abused, that’s a social factor that is taken into account when sentence is passed. Why not brain imaging data too? Why not factors pertaining to brain dysfunction, given that we have found clear and consistent links between brain damage and violent behaviour? Imaging data is no different from data about any other factors that may have constrained a person’s freedom of will-that may have predisposed the individual towards violence.