Evidence of Lies and Rules of Evidence: The Admissibility of fMRI-Based Expert Opinion of Witness Truthfulness

October 30, 2014

Neuroscientists are exploring intriguing technology that some claim will revolutionize the jury’s search for truth. Functional Magnetic Resonance Imaging (“fMRI”) seeks to correlate brain activity with cognitive function. Current research with regard to lie detection indicates that laboratory studies have achieved accuracy rates in excess of 90% in identifying deception and verifying truth in study participants. But how likely will this new technology be useful in the context of the rules governing the impeachment and rehabilitation of witnesses at trial? Does the new technology meet the reliability standards demanded of expert scientific opinion? Has the neuroscience community generally accepted the reliability of fMRI as a lie detector? Will professional opinions on witness truthfulness actually help the jury in its fact-finding role? Or, will it confuse and confound the jury in its essential task of reaching a
Judicial scrutiny and scholarly commentary to date has focused on the reliability of expert opinion and whether the neuroscience community has generally accepted this new application of fMRI with little consideration of other evidentiary requirements that may limit expert opinion testimony of witness truthfulness. This Article identifies thirteen impediments to admissibility and presents them under five major categories: (1) the regulation of impeachment and rehabilitation of witnesses; (2) the requirement that expert testimony help the jury to understand the evidence or decide a fact in issue; (3) the rule requiring expert testimony to be based upon reliable principles and methods; (4) the requirement in some jurisdictions that novel scientific principles be generally accepted by the relevant scientific community; and (5) the balancing of unfair prejudice and probative value of the opinion testimony.