Watching only a few episodes of Law & Order might convince you that the latest, high-tech neuroscience techniques are used in court as often as L&O reruns are on TV, but this won't be true until the use of these technologies becomes less expensive. No Lie MRI, which claims it can use fMRI as a more accurate polygraph, charges $30/min. Cephos, a similar company, doesn't give prices on its website, but does mention that there are additional costs for expert testimony. No Lie MRI's site claims the company's services could one day improve "investor confidence" and "how wars are fought," and individuals undoubtedly dream of a day they could scan a spouse's or teenager's brain, but for now, these companies' main customers seem to be defense attorneys desperate to keep their clients off death row. In addition to detecting lies, brain scans have been presented as evidence that a defendant cannot be held culpable for a crime due to neurological defects. This type of evidence has also mainly been used in death penalty cases and remains controversial.
Of course, the death penalty itself is controversial as well. A July 2008 survey of registered voters showed that 63% of Americans are in favor of the death penalty while 29% oppose it. Since it seems that neurolaw currently mainly affects death penalty cases, could the use of neuroscience in the court change how Americans feel about the death penalty and how many defendants receive it?
fMRI lie detection is intended to provide evidence of guilt or innocence, so Americans who oppose the death penalty because they fear an innocent person may be put to death may find themselves less resistant to the death penalty when faced with this evidence. However, only 30% of respondents to one survey said they opposed the death penalty for this reason. Furthermore, fMRI lie detection will never be proven 100% accurate. Some opponents of the death penalty may be unpersuaded no matter how low the chance of error may one day be.
Support for the death penalty may decrease if fMRI lie detection becomes widespread because it would be easier to convince the public of an unfair conviction than an unfair exoneration. Even after a conviction based on fMRI evidence, evidence could turn up that proves a death row inmate's innocence (newly found DNA evidence or surveillance tapes, for instance). The public's support for fMRI use would surely decrease after such an incident, and because of double jeopardy, it is unlikely that someone found not guilty could later be shown to be guilty. This could lead the public to believe that such technology is more likely to inaccurately show guilt than innocence.
As for scans, a defense attorney could certainly argue that his or her client should not be held culpable because a brain defect "made" the defendent commit the crime. However, the jury might take this information to mean that the defendant has no control over his or her actions, is a danger to society, and should be put to death. Neuroscience will undoubtedly change the nature of the legal system, but how it will change perceptions of the death penalty remain to be seen. After all, the American Psychological Association reported in 2001 that attitudes toward the death penalty have a large genetic component, so American's attitudes may be fairly resistant to change.