He was once a respected pediatrician, loved by patients and their parents for over 30 years. Now Domenico Mattiello faces trial for pedophilia, accused of making sexual advances towards little girls in his care.

Scientific experts will argue in court that his damaged brain made him do it, and his lawyers will ask for leniency.

It's the latest example of how neuroscience - the science of the brain and how it works - is taking the stand and beginning to challenge society's notions of crime and punishment.

The issue has been thrown into the spotlight by new technologies, like structural and functional magnetic resonance imaging (MRI), positron emission tomography (PET) scans and DNA analysis, that can help pinpoint the biological basis of mental disorders.

A series of recent studies has established that psychopathic rapists and murderers have distinct brain structures that show up when their heads are scanned using MRI.

And in the United States, two companies, one called No Lie MRI and another called Cephos Corp, are advertising lie-detection services using fMRI to lawyers and prosecutors.

CRIME AND PUNISHMENT

While structural MRI scans show the structure of a brain and can highlight differences between one brain and another, PET and fMRI scans can also show the brain in action, lighting up at particular points when the brain engages in certain tasks.

But the dazzling new technologies and detailed genetic data leave unanswered the issue of whether criminal courts are the right place to use this new information.

"The worry is that the law, or at least some judges, might be so overawed by the technology that they start essentially delegating the decision about guilt to a particular form of test," says Colin Blakemore, a professor of neuroscience at Oxford University.

The lawyers for American serial killer Brian Dugan, who was facing execution in Illinois after pleading guilty to raping and killing a 10-year-old girl, used scans of his brain activity to argue he had mental malfunctions and should be spared the death penalty. In the event, Illinois abolished capital punishment while he was on death row.

In a court in the Indian city of Mumbai, a woman was convicted of murder based only on circumstantial evidence and a so-called brain electrical oscillations signature profiling (BEOS) test, the results of which prosecutors said suggested she was guilty.

The days when mental capacity for crime is argued over by psychiatrists unaided by sophisticated machinery - such as Friday's verdict that Norwegian mass killer Anders Behring Breivik was sane when he killed 77 people - look numbered.

"All sorts of types of neuroscience evidence are being used for all sorts of types of claims," says Teneille Brown, a professor of law at the University of Utah. "The question is, is this technology really ready for prime time, or is it being abused?"

"ACQUIRED PAEDOPHILIA"

In Mattiello's case, the neuroscientific evidence will come in the form of a full psychiatric and biological analysis including an MRI brain scan that shows a roughly 4 centimeter tumor growing at the base of his brain.

This created pressure inside his skull and "altered his behavior", says Pietro Pietrini, a molecular geneticist and psychiatrist at Italy's University of Pisa who is compiling an expert report on the 65-year-old.

"His previous behavior was completely normal," Pietrini told Reuters. "He was a pediatrician for 30 something years and he saw tens of thousands of children and never had any problem. The question is why, at some point, did someone who has always behaved properly suddenly change so drastically?"

The doctor was arrested in Vicenza, northern Italy, more than a year ago and is undergoing cancer treatment after having the tumor removed. Pietrini is due to see him again next month to continue his assessment and see the effects of the treatment.

The case, which has yet go to court, is strikingly similar to another of "acquired pedophilia" dating back to 2002, in which a 40-year-old married American schoolteacher suddenly became obsessed with sex and began secretly to collect child pornography.

He was eventually removed from the family home for making sexual advances towards his step-daughter and convicted of pedophilia. But later medical examinations found he had an egg-sized tumor in a part of the brain involved in decision-making.

When the tumor was removed, the man recovered from his pedophilic tendencies and was able to return to his family.

Experts are generally agreed that conditions like psychopathy and pedophilia can't be "cured", but in this groundbreaking case it appeared that removing the tumor, and hence the pressure in the brain, may have re-established his ability to control impulses.

As in that case, Pietrini said he and colleague Giuseppe Sartori of Padua University believed Mattiello's tumor "may well have played a role in altering his behavior".

"This is what we will be arguing," Pietrini said. "But of course it will be for the judge to determine to what extent he believes this medical condition played a role."

Oxford's Blakemore, one of the world's leading thinkers in this field, says such cases are "startling".

"It makes one wonder about the notion of responsibility," he said in an interview.

IS "MY BRAIN MADE ME DO IT" A DEFENCE?

And when it comes to prison, should pedophiles, psychopaths and other violent criminals be punished less severely if their behavior can be blamed on biology? Is "my brain made me do it" a defense that warrants recognition with lighter sentences, or even no jail time at all?

"(It) raises the whole issue of what you think sentencing is for," says Blakemore. "Is it about punishment? Is it about retribution? Is it about remediation and rehabilitation? Is it about protecting society? Well, to some extent it's about all of those things."

Recent evidence - from both real and hypothetical cases - suggests judges are sympathetic to neurobiological evidence as mitigation.

A study published in the journal Science this month showed that criminal psychopaths in the United States whose lawyers provide biological evidence for their brain condition are more likely to be sentenced to shorter jail terms than those who are simply said to be psychopaths.

For the study, researchers at the University of Utah tweaked the real-life case of Stephen Mobley, a 39-year-old American who was sentenced to death in 1994 after robbing a Domino's pizza place in Georgia and shooting dead the restaurant's manager.

At his trial, Mobley's lawyer presented evidence in mitigation showing the accused had a variant of a gene called MAO-A that has been dubbed the "warrior" gene after scientists found it was linked to violent behavior.

AGGRESSIVE GENES

In the Science study, judges were given a hypothetical case loosely based on Mobley's, where the crime was a savage beating with a gun, rather than a fatal shooting.

All the judges were told the defendant was a psychopath, but only half were given expert testimony on the genetic and neurobiological causes of his psychopathy. Those who got the neuroscientific evidence were more likely to give a shorter sentence - generally about a year less, the study found.

Pietrini worked on a similar real-life case in Italy in 2009 - thought to be one of the first criminal cases in Europe to use this type of neuroscientific evidence.

It involved Abdelmalek Bayout, an Algerian living in Italy, who was tried and convicted for fatally stabbing a man who teased him in the street.

After conducting a series of tests on the Algerian, Pietrini and colleagues said they had found abnormalities in imaging scans of his brain, and in five genes that have been linked to violent behavior - including MAO-A.

A 2002 study led by researchers at the Institute of Psychiatry at King's College London linked low levels of MAO-A with aggressiveness and criminal behavior in boys who were raised in abusive environments.

Bayout's lawyers got his sentence reduced by arguing that this and other bad genes had affected his brain and were partly to blame for the attack.

WHERE WILL IT END?

Experts say it's almost inevitable that neuroscience and law will become yet more intertwined. After all, while neuroscience seeks to find out how the brain functions and affects behavior, the law's main concern is with regulating behavior.

Yet many are uneasy about the use in courts of law - and in matters of life and death - of basic science that is only just creeping out of the lab.

Observers such as Hank Greely, a professor of law at Stanford University, point out that no scientific peer-reviewed studies have been published demonstrating that BEOS - the brain test used in the Mumbai case - actually works.

Others stress that while genes like MAO-A have been associated with violence, there are also plenty of people with similar genotypes who don't go out and kill, rape or abuse.

"Neuroscience is being used by serious scientists in real labs, but the people trying to apply it in courts are not those same people," says Utah's Brown. "So they're taking something that looks very objective, that looks like gold standard science, but then morphing it into a forensic use it wasn't developed for.

"This isn't snake-oil science. It's real science. But it's being misapplied."

Seena Fazel, a clinical senior lecturer in forensic psychiatry at Oxford University, says he's uncomfortable with the long-term implications and wonders where it will end.

There are already known biological bases for many brain disorders criminals suffer from, including drug addiction, alcoholism and antisocial personality disorder, which is thought to affect up to half of all those in prison.

"If psychopathy reduces your sentence because it has a biological basis, why shouldn't these other more common conditions also result in reduced sentences? The problem here is where do we draw the line?"

RELATED STORIES