FMRI and BF meet FRE: brain imaging and the federal rules of evidence.

I. INTRODUCTION Picture this: a party to a lawsuit proposes to show jurors images of a human brain to support its claim or defense. The other party objects, and the trial judge must make a ruling. What determines how the judge will rule? That is the question I attempt to address. I begin in Part II by describing very briefly some existing methods of brain imaging-how they work and what they try to do-and cataloging some possible uses of these methods in courtrooms. Part III discusses current legal standards of admissibility of scientific evidence under the Federal Rules of Evidence (FRE). Part IV examines the particular problem of scientific evidence offered to establish that a person was or was not telling the truth. Part V provides a brief history of some past attempts to introduce brainimaging evidence into courtrooms. The article concludes with some general comments on the issues facing judges when parties to lawsuits offer brainimaging evidence. I will not try to evaluate the science underlying the various brain-imaging methods for the good reason that I am not trained or otherwise competent to do so. I will try to stick to matters of law-to describe court rulings and the approaches and standards derived from those rulings. I will try to avoid making predictions, but I will have to settle for keeping predictions to a minimum. II. SOME EXISTING BRAIN-IMAGING METHODS AND THEIR POSSIBLE USES IN COURTROOMS A. CURRENT METHODS OF BRAIN IMAGING Although I briefly describe below the existing brain-imaging methods I have in mind when discussing legal standards for admissibility as evidence in courtrooms, the goal of this article is not to make predictions about the admissibility of these particular methods as they currently exist or as they develop in the future. Rather, I hope to provide information about and analysis of the more general framework of evidence law by which all these methods, and others not yet developed, have been and will be judged. 1. Functional Magnetic Resonance Imaging (fMRI)1 The science behind fMRI may be sophisticated, but the basic concept is relatively easy to understand. fMRI involves making a series of brain images to show changes in blood levels in the various areas of the brain over time. Researchers hope that use of fMRI will help them to understand better how the brain operates. The more immediate use of fMRI, however, and the use that has generated the most interest and debate about possible courtroom use, is lie detection. The theory is that blood levels show how hard the brain is working and that lying takes more "brain work" than telling the truth.2 2. Positive Emission Tomography (PET)3 Like fMRIs, PET scans attempt to show the brain in action over time. PET scans use radioactivity to map differences in metabolic activity in areas of the brain.4 Again, the assumption is that areas with the most metabolic activity are doing the most work. PET scans can help us to understand which parts of the brain are used for which kinds of mental tasks. 3. Single Photon Emission Computed Tomography (SPECT)5 SPECT scans, like PET scans, use radioactivity to detect brain function over time. SPECT scans are less expensive than PET scans, but do not work as well in mapping brain activity to specific brain areas.6 4. "Brain Fingerprinting" (BF) This method, developed by Dr. Lawrence Farwell, uses EEG (electroencephalographs) sensors to record electric brain signals emitted when subjects encounter various stimuli.7 BF examines multiple EEG responses to stimuli and purports to be able to distinguish between stimuli that are familiar to the subject and stimuli that the subject has not encountered before. Thus, BF purports to be able to determine whether the brain gives an "information present" or "information absent" response to a particular stimulus.8 B. SOME POSSIBLE USES OF BRAIN-IMAGING EVIDENCE IN COURTROOMS I list below some possible uses of brain-imaging evidence in legal disputes, but I am not suggesting that this list is exhaustive. …