Professor Adrian Raine has met more convicted murderers than most. As a neuroscientist interested in criminal behaviour, he has tested hundreds of violent criminals to investigate the murky relationship between brains and aggressive behaviour. And as with many in his field, he risks his work being appropriated by lawyers searching for a possible scientific explanation for their clients' crime.
Raine's latest study will be particularly interesting to lawyers. Instead of scouring prisons for his subjects, the participants were taken from the general community. All had been diagnosed with antisocial personality disorder (APD), a condition characterised by life-long antisocial and often violent behaviour. Although they had not committed the seriously violent crimes of his previous subjects, they had similar violent tendencies.
Controversy is never far away from the interpretation of Professor Raine's findings. His main claim to fame is that he detected physical differences in the front part of the brain above the eyes - the prefrontal cerebral cortex - in violent male offenders compared to other men.
"Our previous research has shown that convicted murderers - really violent offenders - have poorer functioning in the brain's prefrontal cortex," Raine says. Brain imaging techniques showed that just as with the more violent offenders, the APD sufferers had fewer cells in their prefrontal cortex. In this case, a deficit of between 11 and 14 per cent - equivalent to about two teaspoons of brain tissue.
But could Raine's subjects actually be suffering from something other than ADP? Previous studies have been criticised for failing to eliminate the possibility that subjects were, for example, undiagnosed schizophrenics. Raine and his colleagues believe that they have carefully controlled for possibilities such as these, and by doing so have actually strengthened the case for ADP being a disorder in its very own right.
Dr Antonio Damasio, a neuroscientist at the University of Iowa, believes Raine's findings are remarkable. "The result identifies a potential neuropathological signature [for ADP]. If replications indicate that the finding is not present in other psychiatric populations, then we would be dealing with a notable advance in the understanding of mental diseases."
But Dr Damasio is quick to caution. Like all work using the technique functional magnetic resonance imaging (fMRI), the shadow of phrenology is never far away. "Normal or pathologic effects related to a given area are often the result of actions elsewhere in the brain. Whatever explanation we formulate for these disorders will have to take into account factors ranging from the level of molecules and neurons to cultural phenomena that impinge in the life of whole individuals."
So where does work like this leave our notion of personal responsibility for our actions? Next time one of Raine's APD patients commits a crime - as they often do - can we hold them responsible given that they appear to be at a physical disadvantage? Raine's work hasn't yet made it into America's courtrooms, but lawyers are seldom slow in making use of new science. And as the case of "Spydor Cystkopf" reveals, it can be difficult for the legal system to deal with.
In the winter of 1991 Cystkopf, a well off semi-retired advertising executive, had an argument with his wife in their New York apartment. During the argument she scratched his face. Given that Cystkopf's friends later testified that he is an extremely calm man, what happened next is hard to explain.
Cystkopf forced his wife to the floor and strangled her. He then threw the body from the window of their apartment in an attempt to make the death look like suicide.
Unlike most defendants, Cystkopf had the resources to explore any avenue of defence. His lawyer put them to good use. The sudden outburst of violence in a previously calm man pointed to the possibility of some brain dysfunction. A brain scan revealed a cyst (hence the pseudonym given to "Cystkopf" by the medical profession) underneath the left half of his frontal lobe which had been present since childhood.
This was enough for him to be referred to Dr Damasio, one of America's leading neuroscientists. Dr Damasio's report stated, "It is reasonable to assume that his inability to respond correctly is due to his long-standing neurological condition." Dr Damasio's evidence never made it to court, however. The prosecution uncovered evidence of heavy gambling debts and allegations that Cystkopf tried to persuade his former wife to commit suicide. He pleaded guilty.
So how should the courts deal with a case such as Cystkopf's? If the prosecution hadn't uncovered evidence of his debts should Dr Damasio's evidence have been used in court? Although the conditions Raine has studied are different from Cystkopf's, both involved dysfunctions in the frontal lobe. Should juries be expected to take into consideration damage to this area?
"We are talking of a predisposition to antisocial behaviour," says Raine of the effect of prefrontal damage. "Some people who have prefrontal deficits do not become antisocial, and some antisocial individuals do not have prefrontal deficits. It's important to make clear that biology is not destiny."
The question of biology and destiny is especially relevant in the case of Cystkopf. More than 4,000 people in New York state would be expected to be suffering from similar cysts. And despite the strong link between APD and the brain's frontal lobe, the existence of APD can be predicted equally well by a collection of 10 "psychosocial risk factors" as it can by the biological deficits. Because mild frontal lobe damage is only one possible cause of violent behaviour, it is unlikely it could be used to acquit someone of a crime. But should it somehow "explain" a crime and lead to a lesser sentence?
Despite the work of Raine and others, the mechanisms by which frontal lobe deficiencies influence criminal behaviour are still unclear. How could deficiencies in a person's frontal lobe predispose them to violence? Linking anatomy to behaviour is a difficult task in any area of the brain, but especially so in the frontal lobe. Neuroscientists know it plays a critical role in a range of abilities, including regulation of aggression, but because the frontal lobe has connections with so many parts of the brain it is impossible to ascribe a single function to it.
Raine is working on several theories, perhaps most the interesting of which concerns the need for an "arousal fix". Psychologists have wondered for a long time if the antisocial behaviour of APD patients was linked to low levels of arousal. Perhaps APD sufferers are unconsciously trying to compensate through stimulation-seeking? "For some kids," says Raine, "one way of getting an arousal-jag is by robbing stores or beating people up."
However Raine's work develops, the use of neurological evidence in a criminal court is always going to be controversial. But if a defendant can pay for it, stopping a neuroscientist testifying may be difficult.
The writer works on the Wellcome Wing Project at the Science Museum in London