During the summer of 2010, John McCluskey committed a crime in Arizona that a jury there might normally view as warranting the death penalty; he carjacked a vacationing couple who were in their 60s, shot them, and left their bodies in a trailer that he set on fire. Yet the defense’s strategy to use brain science — along with other evidence — to argue that mitigating circumstances led to this heinous act, created enough doubt in the jury to sway them from unanimously delivering a death penalty verdict.
“What they found, in a nutshell, was a few structural abnormalities in his brain,” Kent Kiehl, a neuroscientist at the Mind Research Network and University of New Mexico, told Wired magazine. Kiehl went on to explain that the neurological premise of the defense’s argument was that imbalanced brain activity made McCluskey more impulsive and likely to have a skewed emotional regard of his own actions. The defense also factored in McCluskey’s breech birth, abuse as a child, and problems with addiction to argue that his actions weren’t solely based on criminal intent, rendering consideration of the death penalty unjustified.
When it came to McCluskey’s neurological assessment, the defense pointed out several aspects of his brain that were abnormal and, thus, would negatively impact his behavior. Firstly, they identified damage to his cerebellum, which is primarily understood as a part of our brain that is important for coordinating movement. The lawyers claimed that McCluskey suffered from cerebellar cognitive affective syndrome (CCAS), which has been associated with problematic planning and behavior control.
The defense also used MRI scans to show that McCluskey had abnormally small superior frontal lobes. Ruben Gur, an expert witness from the University of Pennsylvania with a background in neuropsychology, explained to Wired that this region is important in “putting your action in context, in the ability to control your behavior, especially when under emotional stress or arousal.”
According to Wired, Gur’s assessment of McCluskey’s PET scans also revealed an overly active amygdala, which is a region that is involved with fear and emotion. When this part doesn’t function as it should, it could lead to a heightened state of alarm. Normally a brain region known as the frontal lobe modulates this response, but McCluskey’s scans showed that this area was failing in its duty to inhibit the “primitive emotional impulses emanating from the amygdala,” Gur stated in a report submitted to the court.
Gur also identified abnormalities in parts of the brain known as the parietal lobe and corpus callosum — the latter being a crucial super highway of communication between the two hemispheres of the brain. Impaired reasoning can result if these regions of the brain don’t do their job. Altogether, the defense used PET scans to convince the jury that McCluskey’s misguided behavior partly stemmed from 10 areas of his brain having below-average activity and 17 other areas being hyperactive.
The prosecution argued against this neurological assessment by showing that McCluskey was capable of conducting numerous tasks, such as running a drug dealing operation in prison, which requires brain regions that the defense argued were not functioning properly.
Increasingly, lawyers are using scans to make the case that their client has an underdeveloped or unhealthy brain that prevents them from clearly making decisions when, for example, carrying out a crime or pleading guilty, NPR recently reported. Nita Farahany, a professor of law and philosophy at Duke University, who studies how brain science is increasingly used in court, told NPR that neuroscience is presented in approximately 5 percent of murder trials. "There's a steady increase of defendants seeking to introduce neuroscience to try to reduce the extent to which they're responsible or the extent to which they're punished for a crime," she said.
"It seems like judges are particularly enamored with the adolescent brain science," she added. "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."