Last week, Alan Alda stopped by the McGovern Institute for Brain Research at MIT to promote his newest PBS documentary, Brains on Trial. The two part series seeks to explore how advancements in neuroimaging technology might one day impact the criminal justice system. (You can watch the documentary here.) Joining Alda in a panel discussion were Robert Desimore and Nancy Kanwisher of MIT, Joshua Greene of Harvard, Bea Luna of the University of Pittsburgh, and Stephen Morse of the University of Pennsylvania.

The documentary centers on a mock criminal trial over which Judge Rakoff of the Southern District of New York (brother of HLS’s own Todd Rakoff) presides. Alda uses the trial to demonstrate how current brain scanning technology–specifically functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG)–might assist us in answering key questions that arise in most criminal cases. Part 1 focuses on the trial phase and how this technology might be used to determine if a witness is lying or telling the truth, if an eye witness actually remembers the defendant, or if the memory of the crime is stored in the defendant’s brain.

While Alda expresses a fair amount of optimism in the documentary, the panelists seemed to agree that there was no foreseeable possibility of incorporating fMRI or MEG to answers these questions. Nancy Kanwisher emphasized that current research is not close to isolating a brain pattern that is unique to the act of lying. The brain pattern that is used to identify lying in contemporary neuroscientific studies also shows up when someone is taking more effort to say something, regardless of whether it is true or false. As Professor Kanwisher points out, the extreme pressures of a trial situation might lead a defendant to express this brain pattern even as she truthfully denies involvement in the crime.

Moreover, several panelists reiterated that the fMRI and MEG scans were not nearly reliable enough to outweigh the prejudice they might introduce into the jury’s decision-making. In discussing his research in the documentary, Steven Laken of Cephos Corporation states that under study conditions he is able to accurately identify when a subject was lying or telling the truth only 90% of the time. One would expect the conditions of a criminal trial to decrease the effectiveness of such technology even further. Stephen Morse drew an analogy to polygraph evidence, which was similarly unreliable but often blindly trusted by juries because it was presented under the aegis of ‘science.’

Professor Morse also rightly pointed out that scanning a defendant’s brain for memories of the crime would raise serious constitutional concerns. The Fifth Amendment protection against self-incrimination would seemingly shield a defendant from having to participate in an fMRI or MEG scan against her will, but it is of course unknown for certain.

Part 2 of the documentary focuses on how neuroimaging might assist a judge at sentencing. Here, the panelists seemed to believe that there was a stronger possibility that fMRI and MEG technology might one day play a role. Both Professor Morse and Joshua Greene referenced research demonstrating that neuroimaging could be useful in predicting which rehabilitative programs will work for particular defendants.

The documentary is highly recommended for those interested in learning more about the intersection of neuroscience and criminal law. As he has demonstrated with PBS’s Scientific American Frontiers and NPR’s Science Friday, Alan Alda has an incredible knack for presenting scientific material in a digestible format for lay audiences.