I was asked by a criminal attorney to conduct a neuropsychological evaluation on his client Matthew, a 29-year-old drug dealer who murdered his partner after finding out that the victim was skimming from net profits. Matthew’s history of crime ran deep and wide, with a string of charges beginning in mid-adolescence that included assault, criminal threats, robbery and a number of drug charges. Early on in elementary school, he was identified as emotionally disturbed and impulsive, and to have a learning disability. The attorney already had the results from an MRI, taken after he sustained a concussion from a car accident following his attempt to avoid police arrest on the murder charge. A neurologist retained by the attorney opined that, besides the concussion, the paralimbic area of Matthew’s brain was reduced in volume and expected blood flow, which was developmental in nature and not due to his concussion. This area involves the orbital frontal and medial cortex, areas that regulates emotions and behavior.
Matthew’s attorney was inspired by the results of neuroscientific studies that found psychopaths and individuals who chronically break the law had observable deficits in their frontal-paralimbic cortex, which undergirds their impulsiveness and lawless conduct. He reasoned that Matthew’s condition was akin to a developmental disorder such as autism, which should mitigate or possibly excuse him from a guilty verdict. He asked me to conduct a comprehensive neuropsychological evaluation and opine on the extent of his client’s neurocognitive and emotional deficits, especially addressing his impulse control. He wanted to know if Matthew had a diagnosible neurocognitive disorder and, if present, how it affected his judgment and behavior at the time of the homicide.
My neuropsychological evaluation of Matthew included an extensive interview regarding his developmental history and the completion of a structured interview to assess for psychopathy, comprehensive neuropsychological testing and a probing examination of his thinking at the time of the homicide. I concluded that the defendant met criteria for the diagnosis of psychopathic personality. This finding was consistent with his history of impulsive aggressiveness dating back to his adolescent years and his history criminal mischief, including the sale of drugs. The neuropsychological test results confirmed that Matthew had a mild neurocognitive disorder with functional limitations in his self-control, judgment and in his attention capacities, consistent with the MRI findings.
Even so, I had to be the bearer of bad news to the attorney. In my opinion, Matthew’s functional limitations were not part of his homicidal behavior. During the examination, Matthew revealed that the killing was planned and not the result of a rage reaction or an impulsive act. He set his partner up to meet with him in a private location and tortured him before stabbing him in the chest. His neuropsychological status did not account for the deliberateness of his state of mind at the time of the killing. Matthew felt wronged livid, but he was fairly judicious in his planning it out. Deep grievance or a sense of having been betrayed are not exculpatory states of mind: if they were so, the lion’s share of interpersonal violence would qualify.
Matthew’s attorney, though, was not wrong in his interpretation of the scientific literature on MRIs and psychopathic behavior. A substantial number of neuroscientists argue that most criminal behavior is biologically determined by dysfunctional brain activity. They cite a number of etiologies (genes, in utero deviations, head injury, etc.) which compromises conscious control of individual behavior. These researchers assert that free will is an illusion. Asking a psychopath to follow social norms, the argument goes, is like asking someone with Parkinson’s disease to stop shaking.
The MRIs of psychopaths do show abnormalities (e.g., reduced cortical volume) in the paralimbic area, which is responsible for the executive control of behavior. This area of the cortex is also richly connected to the emotional and pleasure centers set deeply within the brain, and responsible for putting the brakes on actions on those centers based solely on immediate desire or impulse. Those with deficits in this complex network are more prone to violate social and interpersonal norms. In Matthew’s case, his history suggests such a proneness. However, I did not find evidence of a direct link between Matthew’s neurocognitive limitations and development and his homicidal behavior in this instance. The killing and torture were deliberate and premeditated, and he exercised sound judgment in its planning.
A close look at the MRI literature raises doubts about the robustness of findings regarding the nexus between MRI and psychopathy. Recent scientific literature reviews found the evidence for MRI data to have questionable validity. Many imaging studies have a small sample size, which means the ability of their results to apply generally to all psychopaths is limited. Most MRI studies have not been replicated, and those that have yielded contradictory findings. This is due to a number of issues. Most importantly, some studies have found no significant difference in cortex activity, including the paralimbic area, between psychopaths and normal individuals. One recent meta-analytic investigation (a study designed to summerize the results of aggregated research investigations) concluded that there is no consistent evidence to suggest that psychopathy is associated with specific MRI findings or a functional neuropsychological profile.
Unlike diabetes, which is caused by an immune system that destroys beta cells of the pancreas, the brain doesn’t cause psychopathy. All behavior, including psychopathic behavior, is triggered by something, which is a complex combination of biological, psychological and social forces divined to shape the individual. In Matthew’s case, it wasn’t his disordered neurocognitive faculties that cause him to kill. He deliberated and employed his functional capabilities in order to exact revenge and exercise his rage. It wasn’t simply a disordered brain network doing it.
I’m reminded of a quip attributed to the well-known psychologist Jerome Kagan that the most corrupt people he knew had perfectly functioning brains.
Jalava, J., Griffiths, S., & Larsen, R. R. (2023). How to keep unreproducible neuroimaging evidence out of court: A case study in fMRI and psychopathy. Psychology, Public Policy, and Law, 29(1), 1-18
Hanlon, R. E., Brook, M., Stratton, J., Jensen, M., & Rubin, L. H. (2013). Neuropsychological and intellectual differences between types of murderers: Affective/impulsive versus predatory/instrumental (premeditated) homicide. Criminal Justice and Behavior, 40(8), 933-948.
Kiehl, K. A. (2006). A cognitive neuroscience perspective on psychopathy: Evidence for paralimbic system dysfunction. Psychiatry research, 142(2-