This is the question asked in the May 2007 issue of The Scientist, which discusses the recent commercialisation of fMRI for lie detection, and concludes with a good summary of the persistent problems using this technology in forensic contexts:
[…] in reality, a nonconsensual testtaker need only move his or her head slightly to render the results useless. And there are other challenges. For one, individuals with psychopathologies or drug use (overrepresented in the criminal defendant population) may have very different brain responses to lying, says [New York University Psychology prof Elizabeth] Phelps. They might lack the sense of conflict or guilt used to detect lying in other individuals. […]
If a person actually believes an untruth, it’s not clear if a machine could ever identify it as such. Researchers including Phelps are still debating whether the brain can distinguish true from false memory in the first place. […]
Jed Rakoff, US District Judge for the Southern District of New York, says he doubts that fMRI tests will meet the courtroom standards for scientific evidence (reliability and acceptance within the scientific community) anytime in the near future, or that the limited information they provide will have much impact on the stand.
[…] According to Rakoff, the best way to get at the truth in the courtroom is still “plain old cross-examination.” And in the national security sphere, there’s “much more to detecting spies than the perfect gadget,” [Marcus Raichle, professor at the Washington University in St. Louis School of Medicine] agrees. “There’s some plain old-fashioned footwork that needs to be done.”
- Hat tip to Mind Hacks (11 May), which has a detailed commentary on the article.