Through a Scanner Darkly: Functional Neuroimaging as Evidence of a Criminal Defendant's Past Mental States

As with phrenology and the polygraph, we are again confronted with a device that the media claims to be capable of reading our minds. This new device is functional magnetic resonance imaging ("fMRI"), and it is currently being introduced to negate a criminal defendant's mens rea, such as the specific intent to kill. In this paper we will demonstrate that functional brain images should not currently be admitted into courts for this purpose. We will do so by walking through each step of the imaging methodology in plain terms, making it clear why the brain images are minimally probative when introduced to prove a defendant’s mens rea, and almost certainly substantially more prejudicial than probative on balance. Our commitment to staying close to the science is what separates our article from others, as the previous articles do not spend enough time engaging with the methodology, and in so doing they espouse a far too rosy picture of its probative value. While further research needs to be conducted on mock jurors, preliminary findings suggest that the mere presentation of brain images can make a bad argument appear more sensible. We address other forms of prejudice as well, such as fMRI's potential to mislead jurors and waste the court's resources. As the methodology may one day improve such that the probative value is no longer eclipsed by the extreme potential for prejudice, we offer at the end a non-exhaustive checklist that judges or counsel can use to authenticate the functional brain images and assess the weight these images are to be accorded by fact-finders.