The Brain on Trial

David Eagleman thinks that advances in neuroscience should transform our criminal justice system. Writing in The Atlantic, Eagleman emphasizes how genetic and environmental factors influence cognitive function:

We are each constructed from a genetic blueprint, and then born into a world of circumstances that we cannot control in our most-formative years. The complex interactions of genes and environment mean that all citizens—equal before the law—possess different perspectives, dissimilar personalities, and varied capacities for decision-making. The unique patterns of neurobiology inside each of our heads cannot qualify as choices; these are the cards we’re dealt.

Because we did not choose the factors that affected the formation and structure of our brain, the concepts of free will and personal responsibility begin to sprout question marks. Is it meaningful to say that Alex made bad choices, even though his brain tumor was not his fault? Is it justifiable to say that the patients with frontotemporal dementia or Parkinson’s should be punished for their bad behavior?

It is problematic to imagine yourself in the shoes of someone breaking the law and conclude, “Well, I wouldn’t have done that”—because if you weren’t exposed to in utero cocaine, lead poisoning, and physical abuse, and he was, then you and he are not directly comparable. You cannot walk a mile in his shoes.

The legal system rests on the assumption that we are “practical reasoners,” a term of art that presumes, at bottom, the existence of free will. The idea is that we use conscious deliberation when deciding how to act—that is, in the absence of external duress, we make free decisions. This concept of the practical reasoner is intuitive but problematic.

The “practical reasoner” assumption is, of course, fundamental to much of economics as well. Used thoughtfully, it’s extremely useful for examining how reflective, ends-oriented agents behave. But it’s problematic, to say the least, if we assume that everyone is always a rational actor.

Eagleman argues that the criminal justice system should be sensitive to the cognitive differences among people. Some people murder as the result of calculated, rational decisions, but others murder because brain tumors destroy their ability to control themselves. Those differences matter when thinking about deterrence, treatment, and punishment.