Guilt or innocence, one might say, is all in the mind. After all, there are very few crimes that can be committed without the requisite mens rea, or mental state. If we’re going to punish someone, their acts cannot have been mere accident. We want to know that they had some knowledge that their actions could cause harm, and we want that awareness to be sufficiently high as to require punishment.
The standard criminal levels of mens rea are “negligence” (you ought to have known bad things could happen), “recklessness” (you had good reason to believe that bad things would probably happen), “knowledge” (bad things were probably going to happen), and “intent” or “purpose” (you wanted bad things to happen). If your foot kicks someone in the ribs while you’re falling downstairs, you’re not a criminal. But if you kick someone in the ribs because you don’t like them, then society probably wants to punish you.
We cannot know what anyone was thinking when they did something, however. So we rely on jurors to use their common sense to figure out what an accused must have been thinking at the time.
In recent years, however, there have been enormous advances in neuroscience. Brain scans, the software that processes the data, and good science have approached levels that would have been considered science fiction as recently as the Clinton years. Experts in the field can see not only how the brain is put together, but also what an individual brain is doing in real time. Experimental data show which parts of the brain are active when people are thinking certain things, with good detail.
Functional magnetic resonance imaging (fMRI), in particular, can act as a super lie-detector. Instead of measuring someone’s perspiration and heart rate while they answer questions during a polygraph exam, fMRI looks at actual real-time brain activity in areas having to do with logic, making decisions, perhaps even lying. Experimental data of large groups is pretty good at identifying what parts of the brain are associated with different kinds of thinking.
Every brain is slightly different, of course. Brain surgeons have to learn the individual brain they’re operating on before they start cutting. So general group data don’t translate to an individual person 100%. So any lie-detector use for fMRI would have to require some baseline analysis before proceeding to the important questions.
The issue is whether it will be admissible in court. Polygraph tests generally aren’t admissible, because they’re more an art than a science. But fMRI is all science. In addition, brain scans are already widely admissible for the purpose of reducing a sentence because the defendant had damage to his brain. As forensic neuroscience expert Daniell Martell told the New York Times in 2007, brain scans are now de rigeur in capital cases. In Roper v. Simmons, the Supreme Court, ruling that adolescents cannot be executed, allowed brain scan evidence for the purpose of showing adolescent brains really are different.
Outside the United States, brain scans have already begun to be used by the prosecution to show guilt. In India, a woman was recently convicted of murdering her ex-boyfriend with the admission of brainwave-based lie detection. There was other evidence of guilt as well, including the fact that she admitted buying the poison that killed him. But the brainwave analysis was admitted.
There are deeper policy issues here. Is reading someone’s brain activity more like taking a blood sample, or more like taking a statement? The Miranda rule is there, at heart, because we do not want the government to override people’s free will, and force them to incriminate themselves out of their own mouths against their will. That’s why the fruits of a custodial interrogation are presumed inadmissible, unless the defendant first knowingly waives his rights against self-incrimination. And because the DNA in your blood isn’t something you make of your own free will, by taking a blood sample against your will the government has not forced you to incriminate yourself against your will.
So is a brain scan more like a blood sample? Is it simply taking evidence of what is there, without you consciously providing testimony against yourself? Or will it require the knowing waiver of your Fifth and Sixth Amendment rights before it can be applied?
We’re interested in your thoughts. Feel free to comment.