The emerging academic discipline of neuroethics has been driven, in part, by the recognition that introducing brain scans as legal evidence is fraught with peril. Most neuroscientists think that a brain scan is unable to provide an accurate representation of the state of mind of a defendant or determine whether his frontal lobes predispose to some wanton action.

The consensus view holds that studying spots on the wrinkled cerebral cortex that are bigger or smaller in some criminal offenders may hint at overarching insights into the roots of violence, but lack the requisite specificity to be used as evidence in any individual case. “I believe that our behavior is a production of activity in our brain circuits,” Steven E. Hyman of the Broad Institute of Harvard and MIT told a session at the American Association for the Advancement of Science’s annual meeting earlier this year. “But I would never tell a parole board to decide whether to release somebody or hold on to somebody, based on their brain scan as an individual, because I can’t tell what are the causal factors in that individual.”

It doesn’t seem to really matter, though, what academic experts believe about the advisability of brain scans as Exhibit One at trial. The entry of neuroscience in the courtroom has already begun, big time.

The introduction of a brain scan in a legal case was once enough to generate local headlines. No more. Hundreds of legal opinions each year have begun to invoke the science of mind and brain to bolster legal arguments—references not only to brain scans, but a range of studies that show that the amygdala is implicated in this or the anterior cingulate cortex is at fault for that. The legal establishment, in short, has begun a love affair with all things brain.

Nita Farahany, a professor of law at Duke University, laid out the extent of this infatuation at the recent meeting of the Society for Neuroscience. Helped by a team of 20 law students and undergrads, her research sifted through a massive pool of data to find more than 1,500 judicial opinions from 2005 to 2012 in which an appellate judge mentioned neurological or behavioral genetics evidence that had been used as part of a defense in a criminal case. "The biggest claim people are making is: please decrease my punishment because I was more impulsive than the next person I was more likely to be aggressive than the next person I had less control than the next person," Farahany said at a press conference.

Most cases where neuroscience evidence was introduced resulted in an unfavorable outcome for the defendant, but not all. A bizarre twist has turned up in some cases in which a defendant overturned a decision that went the wrong way by accusing his counsel of failing to look into whether he had some sort of brain abnormality—ineffective counsel typically being an impossibly difficult claim. "If you were asleep as a defense counsel the entire time during the trial, if you were dead during the trial or if you failed to investigate a brain abnormality, you can be found responsible for ineffective assistance of counsel," Farahany said. "That’s a surprising trio."

There's more to come. The arrival of brain science in the courtroom is "challenging fundamental concepts of responsibility and punishment," Farahany said. "Should we hold people responsible for their actions once we understand concepts of impulsivity? Does that square with our fundamental concepts of how and why we hold people responsible?

Brain science has implications as well for the fate of a convicted offender. "This is a country largely focused on retributivism as a basis for punishment," she continued. "Is that a legitimate justification for punishment or do we need to rethink what we do and instead focus more on rehabilitation. That has its own host of different types of social and ethical concerns and a bad history in this country of judges medicalizing behavior." Whichever way things go, jurors and judges are going to be hearing a lot more about amygdalae and orbitofrontal cortices.

Image Source: Nita Farahany, Duke University