American Journal of Law & Medicine

FMRI and BF meet FRE: brain imaging and the Federal Rules of Evidence.(Functional Magnetic Resonance Imaging, Brain Fingerprinting)(Brain Imaging and the Law)


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 brain-imaging evidence into courtrooms. The article concludes with some general comments on the issues facing judges when parties to lawsuits offer brain-imaging 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.



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 (electroencephalographic) 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)


I list below some possible uses of brain-imaging evidence in legal disputes, but I am not suggesting that this list is exhaustive. No doubt other uses are possible today and litigants will think of additional uses in the future. But, in order to provide a context for the legal analysis that follows, it may be useful to have in mind specific uses of brain imaging that have been attempted in the past, and some uses that might be attempted in the future. I group these uses into four categories, although I recognize that line-drawing problems exist among the categories. The purpose of this categorization is to suggest that, as a general matter, problems with the admissibility of brain-imaging evidence increase as one moves from use 1 to use 4.

1. Brain Structure

At the most basic level, a party to a lawsuit might use brain images to show the structure of the brain. The images might show a brain that does not have the shape or size or component portions of a "normal" human brain. Or, a brain image might purport to show damage to a previously normal brain. If the litigant limits the use of the images to showing the basic physical characteristics of the brain, that use might not present any greater problems than if the images were of the heart or lungs or any other internal human organ. On the other hand, to the extent that the brain is significantly more complicated than other human body parts, even conclusions about abnormalities or the fact of damage to the physical characteristics of the brain could be more problematic than for other parts of the body.

2. Moving from Structure to Function

Litigants might attempt to use brain images to go beyond brain structure or condition to make a point about brain function in some way. A litigant might use a brain image to show that a person is "brain dead." Or, a litigant might use a brain image to explain a particular loss of function such as paralysis or inability to speak. This type of use of brain images requires tying the brain, and perhaps certain areas of the brain, to specific human capacities and activities. Brain imaging might also be used to go beyond the fact of damage to show the cause of damage. Again, tying anatomy to function is not a use that is necessarily particular to brains; litigants might want to link loss of function to damage to spinal cords or taste buds or kidneys.

3. Explanation of Behavior; Prediction of Future Behavior

It is probably true that it is difficult if not impossible to distinguish between function and behavior. There are thus line-drawing problems between use 2 and use 3 in my categorization. But what I want to capture with this distinction is the difference between evidence about the brain and evidence about other human body parts. Litigants might attempt to use brain images in ways that they would not use images of the rest of the human anatomy. They might attempt to use brain images to show that a person is experiencing pain. (9) They might offer brain images in arguing for or against a person's responsibility for his or her actions. For example, brain-imaging evidence might be used for or against an insanity defense in a criminal case, (10) or to support or refute a claim of malingering in a civil case. (11) Brain images might also be used to make predictions about future behavior. A litigant might present brain images to establish that a person is dangerous--that he or she is likely to commit violent acts in the future. Litigants might even attempt to use brain images to establish a wide range of propensities or personality traits like recklessness, racism, or unhappiness. (12) Once one moves to these kinds of uses, the possibilities seem unlimited.

4. Lie Detection

At present, the most frequently debated use of brain-imaging evidence is to determine whether a person is telling the truth or lying. Both fMRI and BF are being developed specifically for the purpose of detecting lies. (13) These methods claim to be able to go beyond the old methods not only by being more accurate, but also because they allegedly can determine when a subject is giving incorrect information that the subject actually believes is truthful and accurate. (14) Extensive use of brain images to detect conscious and unconscious lies could potentially transform current methods of fact finding in legal disputes.



FRE 104(a) provides that the judge, not the jury, determines preliminary questions concerning the admissibility of evidence and "the qualification of a person to be a witness." (16) Since brain-imaging evidence seems necessarily to entail presentation by expert witnesses, FRE 702 provides the general standard of admissibility in federal courts. That rule permits "a witness qualified as an expert by knowledge, skill, experience, training, or education" to testify to "scientific, technical, or other specialized knowledge" if that knowledge "will assist the trier of fact to understand the evidence or to determine a fact in issue." (17) In 2000, an amendment to FRE 702 added the following language: "if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case." The 2000 amendment was enacted explicitly in response to Daubert v. Merrell Dow Pharmaceuticals, Inc., (18) the 1993 Supreme Court case that set the current standard for judicial interpretation and application of FRE 702.


The plaintiffs in Daubert were minors born with "serious birth defects." (19) They claimed that Bendectin, a prescription drug sold by Merrell Dow and taken by the plaintiffs' mothers during their pregnancy to control nausea, caused their birth defects. Merrell Dow moved for summary judgment and offered an affidavit from "a well-credentialed expert on the risks from exposure to various chemical substances." (20) This expert "stated that he had reviewed all the literature on Bendectin and human birth defects" and "concluded that maternal use of Bendectin during the first trimester of pregnancy has not been shown to be a risk factor for human birth defects." (21) The plaintiffs offered opinions from eight experts of their own that Bendectin could cause human birth defects. These experts based their opinions on animal studies, on similarities in chemical structure between Bendectin and substances that were known to cause human birth defects, and on reanalyzing earlier human studies. (22)

The federal district judge granted defendant's motion for summary judgment. (23) The Ninth Circuit affirmed, (24) citing Frye v. United States, (25) a 1923 D.C. Circuit case upholding the exclusion of the result of a "systolic blood pressure deception test," (26) commonly known as a "lie detector" test, offered by the defendant in a second-degree murder case. In this short opinion the D.C. Circuit stated that admissibility of "a scientific principle or discovery" (27) depends on whether it is "sufficiently established to have gained general acceptance in the particular field in which it belongs. …

Log in to your account to read this article – and millions more.