Detecting Mens Rea in the Brain

Abstract

Mental states matter. Consequently, we and colleagues designed and executed a brain-imaging experiment attempting to detect-for the first time-differences between mental states relevant to criminal law.

Imagine you've just killed someone in Colorado. It was not your purpose or desire to kill him. Nevertheless, another human being is dead. Arrested and on trial, you do not dispute that your action unjustifiably caused his death. But whereas the prosecutor argues that you knew someone would die as an inevitable by-product of your actions, you assert in your defense that you knew no such thing. Instead (you claim) you were merely reckless. That is, you acted as you did with awareness of a substantial risk that someone would be fatally injured, but without knowing you would kill anyone.

In Colorado, as in many states, there is a huge difference in the sentencing ranges for those convicted of knowing and reckless homicides. In Colorado it means the difference between being sentenced to sixteen to forty-eight years in prison and none.' So your fate rests in the hands of lay jurors who will decide what your mental state was at the time of the fatal act. Specifically: Did you know you would kill someone, or were you merely aware of a risk that you would?

Now, any plausible theory of the point or purpose of meting out punishment to offenders-whether utilitarian, retributivist or expressivist -- will recognize good reasons to condition punishment, or its amount, on the offender's mental state. Mental states matter to the nature and severity of incentives to which human behavior is sensitive, to moral desert, and to society's collective outrage. But, whatever its rationale, the practice of predicating differences in punishment on differences in mental state means that you now face two large problems ignored by our current criminal justice system.