Criminal defense lawyers are increasingly using brain scans and other neurological evidence to defend their clients, according to a new study.
Neuroscience advances in recent years haven't gotten to Minority Report-levels yet, but some scientists believe they can explain—if not predict—criminal activity based on brain scans. The advances have led more lawyers, especially upon appeal, to try to explain their clients' mental makeup as the reason for their criminal behavior.
According to Duke University researcher Nita Farahany, the number of cases in which judges have mentioned neuroscience evidence in their opinion increased from 112 in 2007 to more than 1,500 in 2011. The actual number of cases in which neuroscience evidence is presented is likely much higher because trial data is notoriously incomplete: Many criminal cases are settled outside of court, and the database that Farahany worked from, Westlaw, doesn't contain every criminal case.
"Using this tiny little sliver [of data], the number of cases in which the judges discuss neuroscience is increasing," she told scientists at the Annual Meeting of the International Neuroethics Society last month. "I can't tell you if that's because neuroscience is increasing in the courtroom, but I can tell you that judges are talking about it in more opinions and they're talking about it in much more detail and depth."
The practice has become so commonplace that Hank Greely, director of the Center for Law and the Biosciences at Stanford, says many lawyers would be smart to look into a brain scan for their clients.
"These brain scans are poker chips—if you can throw in some more evidence, it might confuse the jury, and it increases the calculation about when one settles," he says. "Many of these cases are appeals where defendants argue they had ineffective counsel after they've been convicted. They say the trial lawyer was an idiot because he didn't get my brain scanned."
The use of neuroscience as a defense is different from that of a psychological defense, or an insanity plea, because the diagnoses depend on the physical makeup of or damage to the brain, not a psychiatric evaluation.
The science behind these brain scans is still in its infancy, but neuroscientists point to one specific case to prove that a traumatic brain injury or brain abnormalities can cause criminal behavior.
In 2002, a 40-year-old Virginia teacher was caught viewing child pornography and making advances on his stepdaughter. He was convicted of child molestation, but the night before he went to jail, he went to the doctor with a crippling headache and confessed he might commit rape. Doctors found something they didn't expect: A brain tumor.
The cancerous tumor was putting pressure on his orbifrontal cortex, which controls impulse and judgment. The tumor was removed, and the man no longer exhibited pedophilic tendencies. The case was described at the annual meeting of the American Neurological Association. Said one of his doctors: "He wasn't faking."
Since then, scientists have been trying to determine which parts of the brain are associated with certain criminal tendencies, and lawyers have been using their diagnoses to try to mitigate their clients' sentences.
"The biggest way in which neuroscience is being used in the courtroom is to mitigate punishment in one way or another," Farahany says, adding that it's almost exclusively used in death penalty cases. "They say they have a history of brain injury and trauma to say 'I have a different brain than the average person. Because of that difference, I have less control over myself.'"
That argument can keep a prisoner off of death row, but it can also backfire, Greely says.
"The other edge of the sword is that it can show a guy is a 'natural born killer,'" he says. "If he's certain to offend again, the jury could put in a longer sentence or could choose to execute him."
The science also hits on philosophical issues, such as free will. Stephen Morse, associate director of the Center for Neuroscience & Society at the University of Pennsylvania, says ethicists, juries, and scientists have to determine to what degree a brain injury can make someone commit a crime.
"If you don't act intentionally, you're not responsible," he says. "But you can't say 'He has a hole in his head that made him do it.' You have to translate that hole in his head into an excusable condition."
Morse adds that there are thousands of people with a "broken looking brain" who act rational.
Nevertheless, as the science gets better, neuroscience will continue to be used by both criminal attorneys and prosecutors. And the questions that society will have to answer will only get harder, Farahany says.
"There's the risk that by using this evidence, we'll end up in some sort of Minority Report future, where we use this evidence in the place of waiting for a criminal act," she says.
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Jason Koebler is a science and technology reporter for U.S. News & World Report. You can follow him on Twitter or reach him at firstname.lastname@example.org.