“To a neuroscientist, you are your brain; nothing causes your behavior other than the operations of your brain,” Greene says. “If that’s right, it radically changes the way we think about the law. The official line in the law is all that matters is whether you’re rational, but you can have someone who is totally rational but whose strings are being pulled by something beyond his control.” In other words, even someone who has the illusion of making a free and rational choice between soup and salad may be deluding himself, since the choice of salad over soup is ultimately predestined by forces hard-wired in his brain. Greene insists that this insight means that the criminal-justice system should abandon the idea of retribution — the idea that bad people should be punished because they have freely chosen to act immorally — which has been the focus of American criminal law since the 1970s, when rehabilitation went out of fashion. Instead, Greene says, the law should focus on deterring future harms. In some cases, he supposes, this might mean lighter punishments. “If it’s really true that we don’t get any prevention bang from our punishment buck when we punish that person, then it’s not worth punishing that person,” he says. (On the other hand, Carter Snead, the Notre Dame scholar, maintains that capital defendants who are not considered fully blameworthy under current rules could be executed more readily under a system that focused on preventing future harms.)

Image Credit... Brendan Monroe

Others agree with Greene and Cohen that the legal system should be radically refocused on deterrence rather than on retribution. Since the celebrated M’Naughten case in 1843, involving a paranoid British assassin, English and American courts have recognized an insanity defense only for those who are unable to appreciate the difference between right and wrong. (This is consistent with the idea that only rational people can be held criminally responsible for their actions.) According to some neuroscientists, that rule makes no sense in light of recent brain-imaging studies. “You can have a horrendously damaged brain where someone knows the difference between right and wrong but nonetheless can’t control their behavior,” says Robert Sapolsky, a neurobiologist at Stanford. “At that point, you’re dealing with a broken machine, and concepts like punishment and evil and sin become utterly irrelevant. Does that mean the person should be dumped back on the street? Absolutely not. You have a car with the brakes not working, and it shouldn’t be allowed to be near anyone it can hurt.”

Even as these debates continue, some skeptics contend that both the hopes and fears attached to neurolaw are overblown. “There’s nothing new about the neuroscience ideas of responsibility; it’s just another material, causal explanation of human behavior,” says Stephen J. Morse, professor of law and psychiatry at the University of Pennsylvania. “How is this different than the Chicago school of sociology,” which tried to explain human behavior in terms of environment and social structures? “How is it different from genetic explanations or psychological explanations? The only thing different about neuroscience is that we have prettier pictures and it appears more scientific.”

Morse insists that “brains do not commit crimes; people commit crimes” — a conclusion he suggests has been ignored by advocates who, “infected and inflamed by stunning advances in our understanding of the brain . . . all too often make moral and legal claims that the new neuroscience . . . cannot sustain.” He calls this “brain overclaim syndrome” and cites as an example the neuroscience briefs filed in the Supreme Court case Roper v. Simmons to question the juvenile death penalty. “What did the neuroscience add?” he asks. If adolescent brains caused all adolescent behavior, “we would expect the rates of homicide to be the same for 16- and 17-year-olds everywhere in the world — their brains are alike — but in fact, the homicide rates of Danish and Finnish youths are very different than American youths.” Morse agrees that our brains bring about our behavior — “I’m a thoroughgoing materialist, who believes that all mental and behavioral activity is the causal product of physical events in the brain” — but he disagrees that the law should excuse certain kinds of criminal conduct as a result. “It’s a total non sequitur,” he says. “So what if there’s biological causation? Causation can’t be an excuse for someone who believes that responsibility is possible. Since all behavior is caused, this would mean all behavior has to be excused.” Morse cites the case of Charles Whitman, a man who, in 1966, killed his wife and his mother, then climbed up a tower at the University of Texas and shot and killed 13 more people before being shot by police officers. Whitman was discovered after an autopsy to have a tumor that was putting pressure on his amygdala. “Even if his amygdala made him more angry and volatile, since when are anger and volatility excusing conditions?” Morse asks. “Some people are angry because they had bad mommies and daddies and others because their amygdalas are mucked up. The question is: When should anger be an excusing condition?”

Still, Morse concedes that there are circumstances under which new discoveries from neuroscience could challenge the legal system at its core. “Suppose neuroscience could reveal that reason actually plays no role in determining human behavior,” he suggests tantalizingly. “Suppose I could show you that your intentions and your reasons for your actions are post hoc rationalizations that somehow your brain generates to explain to you what your brain has already done” without your conscious participation. If neuroscience could reveal us to be automatons in this respect, Morse is prepared to agree with Greene and Cohen that criminal law would have to abandon its current ideas about responsibility and seek other ways of protecting society.

Some scientists are already pushing in this direction. In a series of famous experiments in the 1970s and ’80s, Benjamin Libet measured people’s brain activity while telling them to move their fingers whenever they felt like it. Libet detected brain activity suggesting a readiness to move the finger half a second before the actual movement and about 400 milliseconds before people became aware of their conscious intention to move their finger. Libet argued that this leaves 100 milliseconds for the conscious self to veto the brain’s unconscious decision, or to give way to it — suggesting, in the words of the neuroscientist Vilayanur S. Ramachandran, that we have not free will but “free won’t.”

Morse is not convinced that the Libet experiments reveal us to be helpless automatons. But he does think that the study of our decision-making powers could bear some fruit for the law. “I’m interested,” he says, “in people who suffer from drug addictions, psychopaths and people who have intermittent explosive disorder — that’s people who have no general rationality problem other than they just go off.” In other words, Morse wants to identify the neural triggers that make people go postal. “Suppose we could show that the higher deliberative centers in the brain seem to be disabled in these cases,” he says. “If these are people who cannot control episodes of gross irrationality, we’ve learned something that might be relevant to the legal ascription of responsibility.” That doesn’t mean they would be let off the hook, he emphasizes: “You could give people a prison sentence and an opportunity to get fixed.”