Since ancient times, people have yearned to attribute human behaviors to a physical source within the head. Recently, neuroimaging technologies have given us the technical ability to look at the living brain, its structures, and some of its functions without the need for invasive procedures. However, the science has a long way to go before these technologies can allow us fully to appreciate the anatomical and physiologic underpinnings of human thoughts, states of mind, motives, will, or behaviors.

In this Article, we use an historical overview to introduce the various new technologies for imaging the brain. Today, the goal of medical science is the same as it has always been: to make medical technologies valid, useful, effective, and safe; and to guide appropriate uses while protecting the public from the misuse of them. Brain images are particularly vulnerable to misuse because they are so visually attractive. This visual power can easily result in misunderstanding about what the images show and what they mean.

Now in its second decade, functional magnetic resonance imaging (fMRI) localizes changes in blood oxygenation that occur in the brain when an individual performs a mental task. Physicians and scientists use fMRI not only to map sensory, motor, and cognitive functions, but also to study the neural correlates of a range of sensitive and potentially stigmatizing conditions, behaviors, and characteristics. Poised to move outside the traditional clinical and research contexts, fMRI raises a number of ethical, legal, and social issues that are being explored within a burgeoning neuroethics literature.

In this Article, I place these issues in their proper historical context. The ethical, legal, and social issues raised by advances in functional neuroimaging are challenging and somewhat distinctive, but they are not entirely new. Earlier methods of body imaging and brain mapping, including phrenology, x-ray, positron emission tomography, and single-photon emission computed tomography, raised similar issues, and perhaps we can use our experiences with these sciences and technologies to help guide current functional neuroimaging policy.

The most important safety decision concerning MRIs was to change the name of the procedure. In the late 1970s, the procedure known as nuclear magnetic resonance (NMR) became magnetic resonance imaging (MRI) because of the negative connotations the word “nuclear” invited. Since then, the use of MRIs has flourished. The procedure is now routinely conducted to make medical diagnoses and to study the brain functioning of healthy volunteers participating in research studies devised by, among others, neuroscientists and economists.

There is nothing intrinsically wrong with changing a procedure's name to respond to a public perception of risk, especially when experts do not share that perception. Yet, while MRIs rarely injure patients or test subjects, there is reason to believe that they have important health and safety consequences not captured in standard informed consent forms. These concerns ironically involve perception of risk. On the one hand, unexpected incidental findings of clinically significant conditions in volunteer research subjects raise a host of ethical concerns.

Neuroimaging has advanced our understanding of how the living brain operates, providing structural and functional images of both healthy and diseased brains. This technology pervades today's society, particularly affecting the legal arena. Some judges argue that scientific evidence, which offers insight into the offender's mental state, is crucial because it is the only means of determining whether an offender's punishment is proportional to his crime. Other judges argue that “objective” evidence does not “wholly determine the controversy,” and focus instead on their duty as gatekeepers to independently evaluate scientific evidence. If courts use brain images to make their culpability determinations more objective and sound, these images must meet pertinent legal standards and shed light on medical conditions. For neuroimaging to meet these legal and medical standards with scientific integrity, scientists must convincingly correlate the dynamic images in a person's brain with the way the person is thinking or acting at that moment.

Brain imaging is one of the most remarkable technological advances towards understanding the relationship of behavior to brain anatomy and physiology. Brain images provide insight to understanding behavior. Additionally, the images themselves carry great impact, particularly when used to show differences in either the anatomy or the biological functioning of two different brains. For these reasons, brain images have increasingly been used in both criminal and civil trials.

After describing some general features of brain imaging, we will focus on functional magnetic imaging (fMRI), as many believe this technology has the most potential for advancing our understanding of how parts of the brain function, including perhaps linking specific functions with cognition and behavior. Brain imaging as a field is vast and therefore our discussion will be limited. First, we will assess the advantages and limitations of fMRI, including research efforts towards standardizing equipment thereby assuring reliability and reproducibility.

In a typical magnetic resonance imaging (“MRI”) study of the brain, subjects are screened for contraindications before being placed in the bore of a large machine, the MRI scanner, which contains a powerful magnet. The scanner produces cross-sectional images of brain tissue as the subjects undergo a series of brief electromagnetic pulses, perceptible only as noise and vibration. If the protocol involves functional MRI (“fMRI”), a popular research technique for obtaining indirect measurements of brain activity, equipment might be used to present stimuli (sounds or pictures) during the scan, but generally the study involves no invasive procedures, no physical discomfort, and no ionizing radiation. Upon completion of the scan, MRI data is transferred to an investigator's computer for further analysis, often in combination with behavioral test results and clinical information obtained from subjects or their medical records.

This procedure sounds benign, and usually is. But an MRI scanner is a powerful medical device, capable of causing serious injury or death if operated carelessly.

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.

We are told that functional magnetic resonance imaging (fMRI) is “not ready for use, despite optimism about its commercial potential.” This is probably true—it is also, in terms of legal analysis, irrelevant. Although the development of fMRI technology is still in its relative infancy, there is no guarantee that the law governing its use will wait for it to grow up. Thus, the recent backlash against the initial flurry of articles, both academic and general, on the promise and legal issues surrounding fMRI is unwarranted. The conclusion that so many—even many of the contributors to this volume—seem to be drawing, namely, that law, as a field, must abstain from analyzing the legal implications of fMRI until those with more scientific expertise deem it ready to look at, is at best wrong and, at worst, irresponsible.

The development of a successful lie detector has been a dream of governments and law enforcement since ancient times. A Hindu Veda written around 900 B.C.E. suggests a strategy for detecting lying behavior in suspects:

Six hundred years later, the Greeks were attempting to detect lies by feeling the suspect's pulse. What is interesting about both the early Hindu and Greek examples is that the methods employed were empirical; the interrogators were looking for physiological changes in the body that corresponded to the mental state in question.

“Illustration” or “map” are among the most frequently used words for translating the Chinese character tu, a graphic representation of any phenomenon that can be pictured in life and society, whether in traditional China or elsewhere. Investigations of the early role of tu in Chinese culture first set out to answer questions about who produced tu, the background of its originator, and the originator's purpose. How were pictures conceptualized? Interpreted? In examining tu, Chinese scholars stressed the relational aspect of tu and shu (writing) to answer both these questions, as well as to the importance of not robbing an image of its overall beauty and life with too much graphic detail. In the West, specific concepts of technical or scientific illustrations did not exist before the Renaissance. With the coming of that age, technical illustration became a specific branch of knowledge and activity, with its own specific goals and ends.

A neurologist with abdominal pain goes to see a gastroenterologist for treatment. The gastroenterologist asks the neurologist where it hurts. The neurologist replies, “In my head, of course.” Indeed, while we can feel pain throughout much of our bodies, pain signals undergo most of their processing in the brain. Using neuroimaging techniques like functional magnetic resonance imaging (“fMRI”) and positron emission tomography (“PET”), researchers have more precisely identified brain regions that enable us to experience physical pain. Certain regions of the brain's cortex, for example, increase in activation when subjects are exposed to painful stimuli. Furthermore, the amount of activation increases with the intensity of the painful stimulus. These findings suggest that we may be able to gain insight into the amount of pain a particular person is experiencing by non-invasively imaging his brain.

Such insight could be particularly valuable in the courtroom where we often have no definitive medical evidence to prove or disprove claims about the existence and extent of pain symptoms.

The centrality of freedom as a philosophical construct is often neglected in contemporary academic circles and popular media outlets when it comes to discussions of crime, criminals, and the criminal law. This is surprising, especially since freedom—its absence or its presence—is an important ethical dimension underpinning all transgressive acts, including delinquency and crime. More specifically, the notion of freedom problematizes wayward conduct because transgression can (and does) emerge from freedom's limits rather than its excesses. What this suggests, then, is that criminality is not necessarily an artifact of one's autonomy gone awry or of making “bad” choices; rather, criminality may be a moment of self-discovery, transformation, and transcendence in which a “critical freedom” is borne. This is a period marked by living life on the edge; of contesting thresholds and boundaries in which “a plethora of original ideas, thoughts, inventions, new forms of resistance, and so forth” emerge.

H.L.A. Hart has stated that certain mental conditions have an “excusing” effect on punishment, whereby “[t]he individual is not liable to punishment if at the time of his doing what would otherwise be a punishable act he is … the victim of certain types of mental disease.” The Supreme Court, however, upheld a state statute allowing for increased “punishment,” in the form of civil commitment, for sexually violent predators who suffer from a “mental abnormality.” Thus, American jurisprudence is faced with a paradoxical role of mental conditions: serving to both aggravate and mitigate sentences. This dual purpose of mental conditions becomes a pressing legal issue as mental conditions associated with brain structure or function become more detectable with the emergence of neuroimaging.

In federal capital sentencing, judges are obligated to consider aggravating and mitigating factors before imposing a death sentence. There are aggravating and mitigating factors that could be implicated by mental conditions, including future dangerousness, and impaired capacity, respectively.