A new report collates some of the latest numbers on how American courts use brain science in trials. We've got the skinny, plus an analysis of the good and bad consequences.

In 2009, officials in Lorain County, Ohio, sued a single mother for permanent custody of her 10- and 11-year-old children, claiming that the mother neglected the children and her boyfriends sexually abused them. Although social workers had provided the mother with parenting classes, she was incapable of doing a better job, the county maintained. Among the evidence officials provided: the fact that when she was 14, the mother had been in a car accident that left her mentally impaired and with a reported IQ of 70.*

The Lorain family case is just one of more than 1,500 United States judicial opinions given between 2007 and 2012 that cite brain science in some way. As brain-measuring technologies have improved, neuroscience arguments have increasingly made their way into the U.S. judicial system, as a few observers have noted. A new report, published last week by the U.S. Presidential Commission for the Study of Bioethical Issues, tallies up specific numbers about how and when neuroscience shows up in court cases. Here are some highlights:

Between 2007 and 2012, the number of judicial opinions citing neuroscience doubled.

Among the cases that invoked neuroscience, about 40 percent were for capital murder.

In the majority of cases, lawyers tried to use brain scans and other evidence to argue for lesser punishments. For example, they could use evidence of brain damage to argue a defendant wasn't able to control or plan what he did.

In 2012, five percent of murder trials and 25 percent of death penalty trials invoked neuroscience to argue for less severe punishments.

Neuroscience doesn't always have to help defendants, however. Prosecutors can use neuroscience evidence to argue that somebody is naturally aggressive or dangerous and needs more restrictive punishment. Indeed, neuroscience worked against the Lorain County mother who had wanted to keep her children.

Neuroscience can even work against lawyers. In the past, courts have found attorneys to be ineffective as counsel when they failed to "investigate a reasonable likelihood of a brain abnormality" for clients facing the death sentence.

The rise in neuroscience in courts warrants some caution. The science for many claims—such as the ability to predict whether someone will commit a crime again in the future, or to objectively measure pain—is still uncertain. At the same time, scientific-looking evidence holds strong sway over judges and juries, studies show. So it's important to avoid hype, and to make sure judges are trained in neuroscience. The good news is that a few organizations already run neuroscience seminars for lawyers and judges, like the American Association for the Advancement of Science and the MacArthur Foundation.

While most news stories—understandably—highlight the dangers of misapplied neuroscience, brain research has done a lot of good for courts, too. Emerging science on how long it takes for teens' brains to mature has played a huge role in making it so that courts now can't sentence children under 18 to the death penalty, or to life in prison without parole. Brain-scanning studies have also helped reveal the implicit biases that everybody has, and often lead to people of color getting harsher punishments than white people for the same crimes. Bringing those biases to light with science is the first step to mitigating them.

*UPDATE — March 30, 2015: The previous version of this story suggested the Lorain County mother was 14 at the time officials sued for custody of her children. She was 14 at the time of her car accident, not at the time of her trial.