The Brain on the Stand

[ Sat. Mar. 10. 2007 ]

How neuroscience is transforming the legal system.

...Two of the most ardent supporters of the claim that neuroscience requires the redefinition of guilt and punishment are Joshua D. Greene, an assistant professor of psychology at Harvard, and Jonathan D. Cohen, a professor of psychology who directs the neuroscience program at Princeton. Greene got Cohen interested in the legal implications of neuroscience, and together they conducted a series of experiments exploring how people's brains react to moral dilemmas involving life and death. In particular, they wanted to test people's responses in the f.M.R.I. scanner to variations of the famous trolley problem, which philosophers have been arguing about for decades. ...

...Michael Gazzaniga, a professor of psychology at the University of California, Santa Barbara, and author of "The Ethical Brain," notes that within 10 years, neuroscientists may be able to show that there are neurological differences when people testify about their own previous acts and when they testify to something they saw. "If you kill someone, you have a procedural memory of that, whereas if I'm standing and watch you kill somebody, that's an episodic memory that uses a different part of the brain," he told me. ...

...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.". ...

...The legal implications of the new experiments involving bias and neuroscience are hotly disputed. Mahzarin R. Banaji, a psychology professor at Harvard who helped to pioneer the I.A.T., has argued that there may be a big gap between the concept of intentional bias embedded in law and the reality of unconscious racism revealed by science. When the gap is "substantial," she and the U.C.L.A. law professor Jerry Kang have argued, "the law should be changed to comport with science" — relaxing, for example, the current focus on intentional discrimination and trying to root out unconscious bias in the workplace with "structural interventions," which critics say may be tantamount to racial quotas. . ...

...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," saysRobert 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.". ...