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This chapter examines the three primary constitutional provisions that limit the gathering and use of neuroscientific evidence by the government: the Fourth Amendment, the Fifth Amendment privilege against self-incrimination, and Due Process. It argues that the way in which the evidence is conceptualized matters a great deal to the amount of constitutional protection it is likely to receive. Uncertainty about how to characterize evidence produced by new technology is an enduring problem in law, and neuroscientific evidence is no exception.

This introductory chapter is an overview on the theory and applications of both the fields of law and neuroscience—‘neurolaw’. It shows how the rapid expansion of neurolaw follows from two claims: that neuroscience provides powerful new evidence about the brain, the mind, and human action; and that this evidence is relevant and highly probative for issues throughout the law. To the extent neuroscientific evidence reveals insights about the mind, decision making, and human behaviour, these insights may provide useful information for explaining, justifying, critiquing, or improving the law’s efficacy and applications in any of its domains. Notwithstanding this broad potential reach, it is not surprising that much of the focus of neurolaw to date has been on criminal law. Accordingly, the chapter provides a framework for categorizing the various claims and arguments about how neuroscience may apply to a legal issue: proof, doctrine, and theory.

This chapter focuses on neuroscience-based lie-detection from the perspective of the policies and epistemic norms underlying the law of evidence and legal proof. It makes the case that in some instances neuroscientific evidence is superior to forms of evidence (scientific and non-scientific) routinely admitted in legal proceedings. In analysing whether neuroscientific evidence should be admitted or excluded in legal proceedings, the chapter asks the important question: ‘compared to what’? Excluding neuroscientific evidence in order to base decisions on evidence that may be more epistemically problematic appears to run afoul of the law’s evidentiary principles and goals. The chapter also emphasizes the extent to which the epistemic norms and standards at issue involve fundamentally legal and not just scientific questions.

The last thirty years have seen an explosion of neuroscience research on how the mind functions. This research paints a revised image of what constitutes human nature and behaviour and how the criminal law can handle those extremes of it that endanger individuals and their society. The revision is important to the criminal law because key criminal law concepts of culpability depend on the internal workings of individuals’ minds. Research into intentionality, consciousness, and brain plasticity are just some examples of areas where new discoveries could help enhance validity and reliability within the criminal justice system. Not surprisingly, lawyers have increasingly introduced neuroscience evidence into the courtroom, a trend suggesting that the complexity of the legal issues raised will only expand as the science progresses. On a more fundamental level, neuroscience is also an excellent resource to revitalize the Model Penal Code’s original focus on subjective determinations of an individual defendant’s blameworthiness, based on that particular defendant’s mental state. Over the last sixty years, the American criminal justice system has become far more punitive, and the subjective inquiry has been overshadowed by a more objective standard that downplays the need to assess individual culpability. The incorporation of modern neuroscience research into the criminal law would bring back a system of justice that more accurately reflects a given defendant’s mental state as well more effectively protects the rest of society. But to benefit from neuroscience in this way, we must first penetrate the mystique that often surrounds the meaning and applicability of the science. We must move on from misconceptions, fears, and misguided debates. And we must realize that although neuroscience brings unique insight to the law, there is nothing about neuroscience that merits unique treatment by the law.