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You can totally see a new version of "Law & Order" or "CSI" coming out of this - neuroscientists are playing a bigger and bigger role in criminal trials. That's because a growing number of defense lawyers are turning to brain science to help their clients. The lawyers say some defendants deserve special consideration because they have brains that are immature or impaired. NPR's Jon Hamilton has more from the Society For Neuroscience meeting in San Diego.

JON HAMILTON, BYLINE: Thousands of brain scientists have come here to listen to some of the world's most prominent researchers. But on Monday, one of the featured speakers was a lawyer. Nita Farahany is a professor of law and philosophy at Duke who has been studying the use of neuroscience in court. She says about 5 percent of murder trials now involve neuroscience, and the number has been rising fast. Farahany says often what's at issue is a defendant's competency.

NITA FARAHANY: So competency to stand trial, meaning you can't assist in your own defense. You weren't competent to have pled guilty because of some sort of brain injury. You weren't competent to have confessed, and so you're trying to suppress evidence that you gave to a police officer when you were immediately arrested.

HAMILTON: Farahany says the approach has been most successful with cases involving teenagers.

FARAHANY: It seems like judges are particularly enamored with the adolescent brain science. Large pieces of their opinions are dedicated to citing the neuroscientific studies, talking about brain development, and using that as a justification for treating juveniles differently.

HAMILTON: Farahany says in one recent drug possession case, lawyers argued that a young man's statement to police couldn't be used even though he'd agreed to talk. The lawyer said that didn't matter because adolescent brains are especially vulnerable to coercion.

FARAHANY: And it worked. The prosecution had to basically start over in developing evidence against the juvenile because they couldn't use his own statements against him.

HAMILTON: What's swaying judges and juries is studies showing that adolescent brains don't function the same way adult brains do. Kristina Caudle, of Weill Cornell Medical College, presented exactly that sort of research here at the Society For Neuroscience meeting. Her study, funded by the NIH, used a technology called functional MRI to look at how the brains of people from 6 to 29 reacted to a threat.

KRISTINA CAUDLE: The typical response, and what you might think is a logical response, is to become less impulsive, to sort of withdraw, to not act when there is threat in the environment. But what we saw was that adolescents uniquely seemed to be more likely to act. So their performance on this task became more impulsive.

HAMILTON: And Caudle found that in adolescents, an area of the brain involved in regulating emotional responses had to work much harder to prevent an impulsive response. Caudles says this sort of study is great for understanding adolescent brain development in a general way.

CAUDLE: What it doesn't do is allow us to predict, for example, whether one particular teenager might be likely to be impulsive, or even to commit criminal behavior.

HAMILTON: And Caudle says she worries that a study like hers could be used inappropriately in court.

CAUDLE: Jurors tend to really take things like MRI scans as fact, and that gives me great pause.

HAMILTON: Joshua Buckholtz, a psychologist at Harvard, says a lot of the neuroscience presented in court is simply unnecessary. He says lawyers don't need neuroscience to make some points.

JOSHUA BUCKHOLTZ: Anyone who's ever had a teenager would be able to tell you that their decision-making capacities are not comparable to adults.

HAMILTON: And Buckholtz says relying on brain science to defend juveniles could have unexpected consequences. For example, he says, what if a prosecutor used an MRI scan to show that a 16-year-old who committed a capital crime had a very mature brain?

BUCKHOLTZ: Would we then insist that we execute that juvenile? Because if our standard is about brain maturity, and we can show that an individual's brain has a maturity level that is comparable to a 45-year-old, are we then bound to go on the basis of that scientific data?

HAMILTON: Buckholtz says it will probably fall to judges to make sure that brain science is integrated into the court system in a sensible way.

BUCKHOLTZ: The more that judges begin to understand what, exactly, a scientific study is and what it says - and what it doesn't say and can't say, I think that we are going to be able to manage this integration better.

HAMILTON: Some universities are trying to help. They have begun offering neuroscience courses designed especially for judges.

HAMILTON: Jon Hamilton, NPR News.

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