You can keep going around in this circle for a long time: Criminals who have brain defects have less control over their actions so judges have a tendency to give them shorter sentences so they are returned sooner to society where they have less control over their actions. That’s at least the in vitro conclusion drawn from a recent experiment that presented neurobiological evidence to judges in hypothetical cases. From Benedict Carey in the New York Times:

“In the study, three researchers at the University of Utah tracked down 181 state judges from 19 states who agreed to read a fictional case file and assign a sentence to an offender, ‘Jonathan Donahue,’ convicted of beating a restaurant manager senseless with the butt of a gun. All of the judges learned in their files that Mr. Donahue had been identified as a psychopath based on a standard interview — that is, he had a history of aggressive acts without showing empathy.

The case files distributed to the judges were identical, except that half included testimony from a scientist described as ‘a neurobiologist and renowned expert on the causes of psychopathy,’ who said that the defendant had inherited a gene linked to violent, aggressive behavior. This testimony described how the gene variant altered the development of brain areas that generate and manage emotion.

The account is an accurate description of one theory of how brain development may underlie aggressive behavior. Its applicability to any individual is unknown, however, given that many other factors could increase the likelihood of violence, researchers said.

The judges who read this testimony gave Mr. Donahue sentences that ranged from one to 41 years in prison, a number that varied with state guidelines. But the average was 13 years — a full year less than the average sentence issued by the judges who had not seen the testimony about genetics and the brain.”