Neuroscience's Uncertain Threat to Criminal Law

Bioethics has its trends, and the latest is "neuroethics." Advances in imaging technology are expanding researchers' ability to observe the brain at work. Popular media and scholarly reports offer sweeping pronouncements about the impact of functional neuroimaging and cognitive neuroscience research on our views about human freedom and responsibility, including accountability for violent behavior. For example, psychologists Joshua Greene and Jonathan Cohen think that advances in neuroscience will show that "[f]ree will as we ordinarily understand it is an illusion," and that this finding will lead us to abandon a justice system that punishes people for blameworthy conduct. (1) If past is prologue, however, dramatic changes in the fundamental concepts and principles governing criminal responsibility are unlikely. The traditional legal approach to assessing responsibility has already survived challenges from many different deterministic accounts of human behavior, both biological and social. At the same time, neuroscientific evidence has affected and will probably continue to affect some applications of the criminal law. A look at two court cases shows how neuroscientific developments could influence decisions about culpability and punishment. Neuroscience Evidence and Capital Punishment The U.S. Supreme Court has established strict constitutional limits on imposition of the death penalty. Execution is reserved for the worst offenders--those exhibiting extreme culpability in committing the most serious crimes. After a defendant is convicted of a crime that could lead to a death sentence, the trial court must have a separate hearing to determine whether to sentence that offender to death. At the hearing, the prosecution and defense present information on aggravating or mitigating circumstances that could strengthen or weaken the case for imposing a death sentence. Death penalty litigation has been the context for many of the efforts to relate neuroscience findings to criminal behavior. One example comes from the Supreme Court. In 2005, the Court held that the Constitution's prohibition against "cruel and unusual punishment" bars states from imposing the death penalty on offenders under age eighteen. Sixteen years earlier, the Court had ruled that execution was an excessive punishment for offenders under age sixteen; Roper v. Simmons raised the age requirement. (2) In Roper, the Court ruled that as a class, juveniles have "diminished culpability" and are not sufficiently blameworthy to deserve society's most severe sanction. In reaching its decision, the Court appeared to draw on material from two amicus briefs--one from the American Psychological Association, and the other from a group of organizations led by the American Medical Association. Both briefs described imaging studies suggesting that in adolescents, parts of the brain associated with impulse control, reasoning, and judgment are less developed than they are in adults. As the AMA brief put it, "To a degree never before understood, scientists can now demonstrate that adolescents are immature not only to the observer's naked eye, but in the very fibers of their brains." (3) But the neuroimaging research was just one factor influencing the Court's decision. In writing for the majority, Justice Kennedy offered an array of reasons to support the Court's position on adolescent capacities. His opinion refers generally to "scientific and sociological studies" that present adolescents as less responsible for their behavior than adults. The opinion specifically cites an article from a developmental psychology journal and makes no explicit reference to neuroscience findings. Thus, it is not clear that the neuroscience evidence carried any special weight in the majority's reasoning about juveniles. Moreover, Justice Kennedy portrayed the expert evidence as consistent with common sense observations. He began the discussion of adolescent culpability by observing that "any parent knows" adolescents are comparatively less mature and responsible than adults. …