One of the most thought-provoking sessions I attended at AAAS was "Nature, Nurture, and Antisocial Behavior: Biological and Biosocial Research on Crime." The three talks encompassed neurocognition, psychobiology, and a range of ethical issues that would make your brain spin if you thought about them hard enough. The topic has great potential for controversy, and it would be easy to interpret some of the data presented as an argument against free will. In some ways, however, I think it illustrates the mistake of thinking of nature and nuture as separate, when in reality the interplay between genetics and environment are inseparable, especially when it comes to criminal activity.

Antisocial behavior on the brain

The University of Pennsylvania's Adrian Raine gave an excellent overview of neurocriminology, which I'll attempt to do justice. Several areas of the brain have been shown to be implicated with antisocial personality disorder (ASPD), commonly known as psychopathy or sociopathy. The frontal cortex is the large part of your brain that is responsible for higher reasoning and behavioral traits, and is one of the areas that has been looked at. It's smaller than normal in individuals with ASPD. Although there is a difference in crime rates between men and women, 77 percent of that difference goes away once you control for frontal cortex volume.

Dysfunction or abnormalities in other brain regions have also been associated with higher rates of crime and ASPD. The septum pellucidum is a region of brain tissue that separates the brain's fluid-filled spaces, called ventricles. During fetal development, there is an opening inside this tissue that usually closes up within the first few months after birth. Individuals for whom this doesn't happen have higher rates of arrest and conviction, and score higher for ASPD.

A key center of emotion activity in the brain, the amygdala, is another important region, and a study comparing ASPD and normal brains found deformations and a significant reduction in volume in the ASPD cohort. These were centered on the basolateral nucleus, which is responsible for fear conditioning. This suggests that one possible source of differences (or one of several interweaving mechanisms) is that ASPD-affected individuals don't form the same sort of response to fear as normal people.

One study that showed this assessed autonomic fear conditioning in 3-year-olds (this is done with a skin conductance test, as you can't put 3-year-olds in MRI machines and expect good results), and then followed up with the subjects 20 years later. Out of 1795 children assessed at age 3, the study was able to follow up with 411. One hundred thirty-seven of these 23-year-olds had criminal records; the remaining 274 had not been in trouble with the law. Looking at their data from 20 years ago, the criminal offenders all showed much poorer fear conditioning.

Does this hint at predisposition, and if it does, what should we as a society do with that information? As we'll see in a bit, attorneys are already beginning to use brain imaging and other neurological data in defense of their clients.

Several other brain abnormalities are linked to other crimes. Spouse abusers tend to show strong limbic and weak frontal activation when presented with aggressive word stimuli, suggesting a hyper-responsiveness to mild provocatory stimulus. White collar criminals have been shown to have increased cortical thickness in the ventral medial prefrontal cortex, the precentral gyrus, and the temporal-parietal junction, compared to age-matched controls. Does this give them some cognitive advantages over the rest of us when it comes to spotting opportunities to benefit?

Not necessarily a life of crime

After Dr. Raine's overview, there were presentations from Nathalie Fontaine of Indiana University, and Dustin Pardini of the University of Pittsburgh Medical Center. Dr. Fontaine's work looked at children with callous-unemotional (CU) traits. Five to ten percent of children, mainly boys, display CU traits, and also experience persistent antisocial behavior. Twin studies point to a genetic component, but there was no genetic or genomic data presented, despite the talk being titled "Genetic and Environmental Influences on the Development of Callous-Unemotional Traits."

Dr. Pardini's talk, which he cautioned was based on very preliminary data, looked at a striking statistic: 80 percent of delinquent adolescents don't offend in adulthood. Are there differences in the 20 percent who do? Brain regions that his study looked at are involved in judging reward and punishment magnitude, as well as prediction error (the ventral striatum), decision-making and set shifting (orbital frontal cortex), performance monitoring (anterior cingulate), and our friend from earlier, the amygdala. By and large, there were significant differences in these brain functions between normal controls, reoffenders, and those who had not been in trouble with the law post-adolescence. But the subjects were only in their early 20s, and the numbers of each group were fairly small, so it's hard to find firm distinctions between the delinquents.

It must be said that all of the data from all three speakers shows correlation, and to my knowledge there is no data showing causation. Furthermore, when thinking about the use of this sort of data as mitigating criminal actions, it's necessary to think about the big picture. A murderer might not have asked to have been born with a smaller frontal cortex or amygdala, but neither would they have asked to grow up in a violent household, a socially deprived neighborhood, an underperforming school, and so on—and all of these have been implicated in the genesis of criminal behavior. Biology and environment are inseparable, and reductionist approaches are inherently flawed.

But biologically deterministic arguments are increasingly being made in court. The most famous, as featured in the New York Times, was the case of Herbert Weinstein. Weinstein strangled his wife and then threw her out of a window in order to make her death look like a suicide. He also had a large cyst in his brain, which the defense team obviously wanted to use as mitigating evidence. The Judge ruled that the brain scans could be shown to the jury, but that they could not be told that cysts like Weinstein's were associated with violence.

Despite this, the prosecution was so afraid of the result that they plea-bargained the case down to manslaughter. I don't have a copy of the image to show you, but it showed a rather large hole where normally you'd see the right frontal cortex. I'm fairly sure that, had I been a jury member, I'd have thought that it was a reasonable argument.

As stated earlier, correlation does not mean causation. But, should causation be shown one day, what would that mean for our legal system and society at large? Should we be doing skin conductivity tests on toddlers and then locking them up based on the results? Should we give more weight to brain scans compared to upbringing just because you can show the former as a pretty picture?

It's not an area that lends itself to easy answers—these are questions that society will have to grapple with as the technology and science gets better. That discussion is already underway at a pretty high level; today the Presidential Commission for the Study of Bioethical Issues meets in Washington, DC, and neuroimaging is one of the two topics slated for discussion. You can even follow along in the fun, as there's a live webstream.