July 1, 2020
New Brain Science Shows Future Dangerousness Cannot Be Predicted in Defendants Under 21
By Dr. Adriana Galván, Dr. Terrie Moffitt, and Dr. Russell Poldrack
Almost three decades have passed since 1993, when Billy Joe Wardlow, who was 18 years old with no prior history of violence conviction, killed Carl Cole in a burglary gone wrong. On July 8, Texas plans to execute him unless the United States Supreme Court intervenes. When Billy went to trial in 1995, Texas law directed that the jury could only sentence a person to death if they did something that we now know to be scientifically impossible: determine that Billy would forever pose a danger to others, even if he never stepped foot outside prison walls.
But in light of what science has now shown about the developing brain, there is a broad consensus in the scientific community that, at the present time, it is impossible to predict whether an 18-year-old‹even one that has committed an act of deadly violence‹is likely to commit acts of violence as a mature adult, or in the words of the Texas statute, pose a ³continuing threat to society.². Therefore, the Texas statute under which Mr. Wardlow was sentenced to death turned on a determination that cannot be made in any objectively reliable or scientific manner.
New technology, and especially brain imaging technology, allows us to study changes in the developing brain, which in turn permits better understanding of the physiological underpinnings for the emotional reactivity and risky decision-making that are characteristic of young people. In particular, our understanding of ³emerging adulthood²‹loosely defined as the teenage years through the early 20s‹has undergone a complete evolution, and there is widespread agreement in the scientific community: the brains of emerging adults are undergoing ongoing maturation in fundamental ways related to emotional regulation, decision-making, and risk-evaluation, even though people in this age range may look (and sometimes act) like adults.
Most importantly for Billy Wardlow is the simple fact that how a person behaves in their teens and early twenties has very limited predictive value for how they will behave once their brain is mature. Almost all adolescents and emerging adults who engage in antisocial or violent conduct desist as a byproduct of the maturation process. Between 25 and 50% of young people who engage in criminal conduct are ³instantaneous desisters,² meaning their first offense is also their last, and the percentage of juvenile offenders who desist from crime by their mid-20s ranges from 85 to 90%, regardless of offense type. Ultimately, of the many young people who engage in crime, no more than 6% are ³lifecourse-persistent offenders² according to co-author of this piece, psychologist Terrie Moffit. And although we can be sure that some young people will remain dangerous, the problem for the criminal-legal system is that there is no way for courts to predict which particular young individuals will fall into that category.
Recent, important neuroimaging studies help explain why. The prefrontal cortex‹an area of the brain associated with reasoning and executive function‹remains developmentally immature until the mid-20s, while at the same time, the brain¹s reward centers are relatively more responsive. Specifically, between early adolescence and emerging adulthood, the ventral striatum within the basal ganglia matures in a way that promotes reward- and sensation-seeking behavior, while developments in the amygdala elevate the brain¹s sensitivity to emotional triggers. At the same time, transformations in the prefrontal cortex and its communication circuitry radically alter the ability of a young person¹s brain to regulate emotions and decision-making. Imaging studies confirm that the development of the function and wiring of the prefrontal cortex develops throughout emerging adulthood, as the brain fine-tunes connections within and between the prefrontal cortex and the basal ganglia.
The results for behavior will be familiar to any parent of a college student: adolescents and emerging adults tend to be more susceptible to emotional reactions and more prone to make impulsive choices‹even when they know better. Some may also be less likely than adults to envision the future and apprehend the consequences of their actions. And importantly, emerging adults are uniquely susceptible to peer influence, and especially when it concerns risky behavior. For these reasons, many types of risky behavior‹for example, binge drinking, criminal conduct, and drug use‹peak in the early- to mid-20s. It is exactly these tendencies that have likely led to noncompliance with pandemic directives and the recent increase in COVID-19 cases among young adults.
What Billy¹s jury in Texas was asked to do in 1995‹predict whether an 18-year-old would be dangerous in the future‹was not possible with any known technology or methodology in existence at the time or available today. It may in fact never be possible, because the human brain is simply not finished growing after 18 years of development. There is no scientific basis from which anyone, the leading scientists in the world included, can predict whether any given adolescent or emerging adult will pose danger years down the road. We hope that the Supreme Court soon recognizes this fact too.
Dr. Adrianna Galván is a Professor of Psychology at the University of California, Los Angeles and the Jeffrey Wenzel Term Chair in Behavioral Neuroscience, and author of ³The Neuroscience of Adolescence² (Cambridge University Press). Dr. Terrie E. Moffitt is Nannerl O. Keohane University Professor of Psychology and Neuroscience at Duke University, and author of ³The Origins of You: How Childhood Shapes Later Life² (Harvard University Press). Dr. Russell Poldrack is the Albert Ray Lang Professor in the Department of Psychology and Professor (by courtesy) of Computer Science at Stanford University and author of ³The New Mind Readers: What Neuroimaging Can and Cannot Reveal about Our Thoughts² (Princeton University Press). Drs. Galván, Moffitt, and Poldrack are signatories to an amicus brief filed in Wardlow¹s case currently pending in the Supreme Court of the United States.