Using Imaging to Identify Deceit: Scientific and Ethical Questions

Chapter 4: Actions Speak Louder than Images

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Emilio Bizzi, Steven E. Hyman, Marcus E. Raichle, Nancy Kanwisher, Elizabeth Anya Phelps, Stephen J. Morse, Walter Sinnott-Armstrong, Jed S. Rakoff, and Henry T. Greely
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Stephen J. Morse


Law must answer two types of general questions: 1) What legal rules should govern human interaction in a particular context? and 2) How should an individual case be decided? Scientific information, including findings from the new neurosciences, can be relevant both to policy choices and to individual adjudication. Most legal criteria are behavioral, however, including, broadly speaking, actions and mental states, and it could not be otherwise. The goal of law is to help guide and order the interactions between acting persons. Consider criminal responsibility, the legal issue to which neuroscience is considered most relevant. Criminal prohibitions all concern culpable actions or omissions and are addressed to potentially rational persons, not to brains. Brains do not commit crimes. Acting people do. We do not blame and punish brains. We blame and punish persons if they culpably violate a legal prohibition that society has enacted. All legally relevant evidence, whether addressed to a policy choice or to individual adjudication, must therefore concern behavior entirely or in large measure.

Behavioral evidence will almost always be more legally useful and probative than neuroscientific information. If no conflict exists between the two types of evidence, the neuroscience will be only cumulative and perhaps superfluous. If conflict does exist between behavioral and neuroscientific information, the strong presumption must be that the behavioral evidence trumps the neuroscience. Actions speak louder than images. If the behavioral evidence is unclear, however, but the neuroscience is valid and has legally relevant implications, then the neuroscience may tip the decision-making balance. The question is whether neuroscientific (or any other) evidence is legally relevant; that is, whether it genuinely and precisely helps answer a question the law asks.

Consider the following examples of both types of questions, beginning with a general legal rule. Should adolescents who culpably commit capital murder when they are sixteen or seventeen years old qualify for imposition of the death penalty, or should that punishment be categorically barred for this class of murderers? Recent neuroscience evidence has demonstrated that the adolescent frontal cortex—roughly, the seat of judgment and behavioral control—is not fully biologically mature. What is the relevance of this information to deciding whether the death penalty should be imposed (see Roper v. Simmons, 2005)?

Now consider the following case of individual adjudication. A sixty-three-year-old businessman with no history of violence or other antisocial conduct has a harsh argument with his wife. During the course of the argument, she lunges at him and scratches his face. He grabs her, strangles her to death, and then throws her out the window of their twelfth-story apartment. The husband is charged with murder. He has the means to pay for a complete psychiatric and neurological workup that discloses that he has a sizable but benign subarachnoid cyst pressing on his frontal cortex. What is the relevance of this finding to his culpability for homicide (see People v. Weinstein, 1992)?


Some common misconceptions bedevil clear thinking about the relevance of neuroscience to law: the belief that scientific discoveries necessitate particular political or legal rules or institutions; the belief that neuroscientific explanation of behavior or determinism generally poses a threat to the legal concept of the person; and the belief that discovery of a cause for behavior means that within our current responsibility practices the agent is not responsible for the behavior, an error I have previously termed the “fundamental psycholegal error” (Morse 1994).

Politics, morality, and law all concern how human beings should live together. They are the domains of practical reason and normativity. As a discipline of theoretical reason, science can help us understand the causal variables that constrain and shape human behavior. Such information can and should inform our reasoning about how to live together, but it cannot dictate any particular answer because how we should live is not a matter of theoretical reason. Some moral theorists believe that we can deduce moral conclusions from facts about the world, but this position is entirely controversial and those who hold it often disagree about specific moral rules. Many people believe that the new neuroscience suggests that a fully physical explanation of all human behavior is possible and that human behavior is as determined as all the rest of the phenomena of the universe. Some conclude in response that we should adopt a fully consequential morality in which concepts like just deserts have no justifiable place, but this conclusion does not ineluctably follow from the truth of universal causation. Even if it did, it would not tell us which goods to maximize, nor would it provide a source of normativity.

To take a more specific example, a recent, provocative study showed that a particular type of brain damage was associated with a willingness directly to take innocent life to achieve a net saving of lives (Koenigs et al. 2007). People without such brain damage were willing indirectly to cause the death of an innocent person to save more lives. If they had to kill the victim directly, however, they stopped calculating and refused to take an innocent life even to save net lives. If the study is valid in real-world conditions, it suggests that people with “normal” brains do not consequentially calculate under some conditions and perhaps it suggests that socializing them to do so might be difficult. But this finding does not necessarily mean that people cannot be socialized to calculate if we thought that such consequential calculation was desirable.

The new neuroscience joins a long list of contenders for a fully causal, scientific explanation of human behavior, ranging from sociological to psychological to biological theories. Such explanations are thought to be threats to the law’s conception of the person and responsibility. Neuroscience concerns the brain—the biological source of our humanity, personhood, and sense of self—and it seems to render the challenge to the legal concept of the person more credible. The challenge arises in two forms. The first does not deny that we are the types of creatures we think we are, but it simply assumes that responsibility and all that it implies are impossible if determinism is true. This is a familiar claim. The second challenge denies that we are the type of creatures we think we are and that is presupposed by law and morality. This is a new and potentially radical claim. Neither succeeds at present, however.

The dispute about whether responsibility is possible in a deterministic world has been ongoing for millennia, and no resolution is in sight (Kane 2005). No uncontroversial definition of determinism has been advanced, and we will never be able to confirm that it is true or not. As a working definition, however, let us assume, roughly, that all events have causes that operate according to the physical laws of the universe and that they were themselves caused by those same laws operating on prior states of the universe in a continuous thread of causation going back to the first state. Even if this is too strong, the universe seems so sufficiently regular and lawful that rationality demands that we must adopt the hypothesis that universal causation is approximately correct. The English philosopher, Galen Strawson, calls this the “reality constraint” (Strawson 1989). If determinism is true, the people we are and the actions we perform have been caused by a chain of causation over which we mostly had no rational control and for which we could not possibly be responsible. We do not have contra-causal freedom. How can responsibility be possible for action or for anything else in such a universe? How can it be rational and fair for civil and criminal law to hold anyone accountable for anything, including blaming and punishing people because they allegedly deserve to be blamed and punished?

Three common positions are taken in response to this conundrum: metaphysical libertarianism, hard determinism, and compatibilism. Libertarians believe that human beings possess a unique kind of freedom of will and action according to which they are “agent originators” or have “contra-causal freedom.” In short, they are not determined and effectively able to act uncaused by anything other than themselves (although they are of course influenced by their time and place and can only act on opportunities that exist then). The buck stops with them. Many people believe that libertarianism is a foundational assumption for law. They believe that responsibility is possible only if we genuinely possess contra-causal freedom. Thus, if we do not have this extraordinary capacity, they fear that many legal doctrines and practices, especially those relating to responsibility, may be entirely incoherent. Nonetheless, metaphysical libertarianism is not a necessary support for current responsibility doctrines and practices. All doctrines of criminal and civil law are fully consistent with the truth of determinism (Morse 2007). Moreover, only a small number of philosophers and scientists believe that human beings possess libertarian freedom of action and will, which has been termed a “panicky” metaphysics (Strawson 1982) because it is so implausible (Bok 1998).

Hard determinists believe that determinism is true and is incompatible with responsibility. Compatibilists also believe that determinism is true but claim that it is compatible with responsibility. For either type of determinist, biological causes, including those arising from the brain, pose no new or more powerful general metaphysical challenge to responsibility than nonbiological or social causes. As a conceptual and empirical matter, we do not necessarily have more control over psychological or social causal variables than over biological causal variables. More important, in a world of universal causation or determinism, biological causation creates no greater threat to our life hopes than psychological or social causation. For purposes of the metaphysical freewill debate, a cause is just a cause, whether it is neurological, genetic, psychological, sociological, or astrological. Neuroscience is simply the newest “bogey” in a dispute about the general possibility of responsibility that has been ongoing for millennia. It certainly is more scientifically respectable than earlier bogeys, such as astrology and psychoanalysis, and it certainly produces compelling representations of the brain (although these graphics are almost always misleading to those who do not understand how they are constructed). But neuroscience evidence for causation does no more work in the general freewill/responsibility debate than other kinds of causal evidence.

Hard determinism does not try either to explain or to justify our responsibility concepts and practices; it simply assumes that genuine responsibility is metaphysically unjustified. For example, a central hard determinist argument is that people can be responsible only if they could have acted otherwise than they did, and if determinism is true, they could not have acted other than they did (Wallace 1994). Consequently, the hard determinist claims that even if an internally coherent account of responsibility and related practices can be given, it will be a superficial basis for responsibility, which is allegedly only an illusion (Smilansky 2000). There is no “real” or “ultimate” responsibility. Hard determinists concede that Western systems of law and morality hold some people accountable and excuse others, but the hard determinist argues that these systems have no justifiable basis for distinguishing genuinely responsible from nonresponsible people. Hard determinists sometimes accept responsibility ascriptions because doing so may have good consequences, but they still deny that people are genuinely responsible and robustly deserve praise and blame and reward and punishment.

Hard determinism thus provides an external critique of responsibility. If determinism is true and is genuinely inconsistent with responsibility, then no one can ever be really responsible for anything and desert-based responsibility attributions cannot properly justify further action. The question, then, is whether as rational agents we must swallow our pride, accept hard determinism because it is so self-evidently true, and somehow transform the legal system and our moral practices accordingly.

Compatibilists, who agree with hard determinists that determinism is true, have three basic answers to the incompatibilist challenge. First, they claim that responsibility attributions and related practices are human activities constructed by us for good reason and that they need not conform to any ultimate metaphysical facts about genuine or “ultimate” responsibility. Indeed, some compatibilists deny that conforming to ultimate metaphysical facts is even a coherent goal in this context. Second, compatibilism holds that our positive doctrines of responsibility are fully consistent with determinism. Third, compatibilists believe that our responsibility doctrines and practices are normatively desirable and consistent with moral, legal, and political theories that we firmly embrace. The first claim is theoretical; the third is primarily normative. Powerful arguments have been advanced for the first and third claims (Lenman 2006; Morse 2004). For the present purpose, however, which is addressed to whether free will is really foundational for law, the second claim is the most important.

The capacity for rationality is the primary responsibility criterion, and its lack is the primary excusing condition. Human beings have different capacities for rationality in general and in specific contexts. For example, young children in general have less developed rational capacity than adults. Rationality differences also differentially affect agents’ capacity to grasp and to be guided by good reason. Differences in rational capacity and its effects are real even if determinism is true. Compulsion is also an excusing condition, but it is simply true that some people act in response to external or internal hard choice threats to which persons of reasonable firmness might yield, and most people most of the time are not in such situations when they act. This is true even if determinism is true and even if people could not have acted otherwise.

Consider the doctrines of criminal responsibility. Assume that the defendant has caused a prohibited harm. Prima facie responsibility requires that the defendant’s behavior was performed with a requisite mental state. Some bodily movements are intentional and performed in a state of reasonably integrated consciousness. Some are not. Some defendants possess the requisite mental state, the intent to cause a prohibited harm such as death. Some do not. The truth of determinism does not entail that actions are indistinguishable from nonactions or that different mental states do not accompany action. These facts are true and make a perfectly rational legal difference even if determinism is true. Determinism is fully consistent with prima facie guilt and innocence.

Now consider the affirmative defenses of insanity and duress. Some people with a mental disorder do not know right from wrong. Others do. In cases of potential duress, some people face a hard choice that a person of reasonable firmness would yield to. These differences make perfect sense according to dominant retributive and consequential theories of punishment. A causal account can explain how these variations were caused, but it does not mean that these variations do not exist. Determinism is fully consistent with both the presence and absence of affirmative defenses. In sum, the legal criteria used to identify which defendants are criminally responsible map onto real behavioral differences that justify differential legal responses.

In their widely noted paper, Joshua Greene and Jonathan Cohen (2004) take issue with the foregoing account of the positive foundations of legal responsibility. They suggest that despite the law’s official position, most people hold a dualistic, libertarian view of the necessary conditions for responsibility because “vivid scientific information about the causes of criminal behavior leads people to doubt certain individuals’ capacity for moral and legal responsibility” (Greene and Cohen 2004, p. 1776). To prove their point, they use the hypothetical of “Mr. Puppet,” a person who has been genetically and environmentally engineered to be a specific type of person. Greene and Cohen correctly point out that Mr. Puppet is really no different from an identical person I call Mr. Puppet2, who became the same sort of person without intentional intervention. Yet most people might believe that Mr. Puppet is not responsible. If so, however, should Mr. Puppet2 also not be responsible? After all, everyone is a product of a gene/environment interaction. But would it not then follow, as Greene and Cohen claim, that no one is responsible?

Greene and Cohen are correct about ordinary peoples’ intuitions, but people make the fundamental psycholegal error (Morse 1994) all the time. That is, they hold the erroneous but persistent belief that causation is per se an excusing condition. This is a sociological observation and not a justification for thinking causation or determinism does or should excuse behavior. Whether the cause for behavior is biological, psychological, sociological, or astrological, or some frothy brew of all of these does not matter. In a causal universe, all behavior is presumably caused by its necessary and sufficient causes. A cause is just a cause. If causation excused behavior, no one could ever be responsible. Our law and morality do hold some people responsible and excuse others. Thus causation per se cannot be an excusing condition, no matter how much explanatory and predictive power a cause or set of causes for a particular behavior might have. The view that causation excuses per se is inconsistent with our positive doctrines and practices. Moreover, if Mr. Puppet and Mr. Puppet2 are both rational agents, the argument I have provided suggests that they are both justifiably held responsible. The lure of purely mechanistic thinking about behavior when causes are discovered is powerful but should be resisted.

At present, the law’s “official” position about persons, action, and responsibility is justified unless and until neuroscience or any other discipline demonstrates convincingly that we are not the sorts of creatures we and the law think we are—conscious and intentional creatures who act for reasons that play a causal role in our behavior—and thus that the foundational facts for responsibility ascriptions are mistaken. If it is true, for example, that we are all automata, then no one is an agent, no one is acting and, therefore, no one can be responsible for action. But none of the stunning discoveries in the neurosciences or their determinist implications have yet begun to justify the belief that we are radically mistaken about ourselves. Let us therefore return to the proper understanding of the relation between neuroscience and law, again using criminal responsibility as the most powerful example.


The criteria for legal excuse and mitigation—like all legal criteria—are behavioral, including mental states. For example, lack of rational capacity is a generic excusing condition, which explains why young children and some people with mental disorder or dementia may be excused if they commit crimes. For another example, as Justice Oliver Wendell Holmes wrote long ago, “Even a dog distinguishes between being stumbled over and being kicked.” Mental states matter to our responsibility for action. Take the insanity defense, for example, which excuses some people with mental disorder who commit crimes. The defendant will not be excused simply because he or she is suffering from mental disorder, no matter how severe it is. The defendant will not be excused simply because disordered thinking affected the defendant’s reasons for action. Rather, the mental disorder must produce substantial lack of rational capacity concerning the criminal behavior in question. All insanity defense tests are primarily rationality tests. Lack of rational capacity is doing the excusing work.

Mental disorder that plays a role in explaining the defendant’s behavior may paradoxically not have any effect on responsibility at all. Imagine a clinically hypomanic businessperson who, as a result of her clinical state, has really high attention, energy, and the like, and who makes a contract while in that state. If the deal turns out to be less advantageous than she thought, the law will not allow her to avoid that contract even though she made it under the influence of her mood disorder. Why? Because the businessperson was perfectly rational when she made the contract. Indeed, her hypomania might have made her “hyper-rational.” Here is another example from criminal law. Imagine a person with paranoia who is constantly scanning his environment for signs of impending danger. Because the person is hypervigilant, he identifies a genuine and deadly threat to his life that ordinary people would not have perceived. If the person acts in self-defense, he is fully rational and his behavior would be justified. In this case, again, the mental abnormality made the agent “hyper-rational” in the circumstances.

Potentially legally relevant neuroimaging studies attempt to correlate brain activity with behavior, including mental states. In other words, legally relevant neuroscience must begin with behavior. We seek brain images associated with behaviors that we have already identified on normative, moral, political, and social grounds as important to us. For example, we recognize that adolescents behave differently from adults. They appear to be more impulsive and peer-oriented. They appear, on average, to be less fully rational than adults. These differences seemingly should make a moral and legal difference concerning, for example, criminal responsibility or the age at which people can drink or make independent health-care decisions. These differences also make us wonder if, in part, neuroanatomical or neurophysiological causal explanations might exist for the behavioral differences already identified as important to us.

Indeed, there is a parallel between the use of neuroscience for legal purposes and the development of cognitive neuroscience itself. Psychology does and must precede neuroscience when human behavior is in question (Hatfield, 2000).2 Brain operations can be divided into various localities and subfunctions. The investigation of these constitutes the field of neuroscience. Some of the functions the brain implements are mental functions, such as perception, attention, memory, emotions, and planning. Psychology is broadly defined as the experimental science that directly studies mental functions. Therefore, psychology is the primary discipline investigating a major subset of brain functioning, including those functions that make us most distinctly human. These are also the types of functions that are therefore most relevant to law, because law is a human construction that is meant to help order human interaction. On occasion, inferring function from structure or physiology might be possible. In most cases, however, general knowledge or conjecture about function guides the investigation of structure and physiology. This will be especially true as we move “from the outside in.” That is, it will be especially true as we study complex, intentional human behavior as opposed to, say, the perceptual apparatus. Lastly, therefore, psychology is the royal road to brain science in those areas that make us most distinctly human and that are most relevant to law.

When we evaluate what might be legally relevant brain science, we will be limited by the validity of the psychology upon which the brain science is based. As most—indeed, as all—honest neuroscientists and psychologists will admit, we wish that our psychological constructs and theories were better than they are. Thus, the legal helpfulness of neuroscience is limited.

Despite the limitations just described, neuroscience can sometimes be of assistance in helping us decide what a general rule should be and in adjudicating individual cases. Identifying brain correlates of legally relevant criteria is seldom necessary, or even helpful, when we are trying to define a legal standard if the behavioral difference is already clear. If the behavioral difference is not clear, then the neuroscience does not help, because the neuroscience must always begin with a behavior or behavioral difference that we have already identified as important.

For example, we have known that the rational capacity of adolescents is different from adults. Juvenile courts have existed for over a hundred years, well before anyone thought about neuroimaging the adolescent brain. The common law treated juveniles differently from adults for hundreds of years before we had any sense of neuroscience. People had to be of a certain age to vote, to drink, to join the army, and to be criminally responsible long before anyone envisioned functional magnetic resonance imaging (fMRI). If the rational capacity difference between adults and adolescents was less clear, then neuroscience could not tell us whether to treat adolescents differently, even if we believed that rationality made a difference. Whether adolescents are sufficiently different from adults so that they should be treated legally differently is a behavioral and normative question in the first instance. Once the behavioral difference is established, at most the neuroscience concerning the biological immaturity of the adolescent prefrontal cortex does nothing more than provide a partial biological causal explanation of a normative relevant behavioral difference.

At this point one might object that the law draws bright, categorical lines when it is responding to behavioral continua and thus the law obscures important individual behavioral and moral differences. For example, although adolescents and adults on average demonstrate rationality differences that we think are morally and legally important, rationality is a continuum capacity and the adolescent and adult curves overlap, especially at the adolescent/adult margin. That is, some adults are less rational than some adolescents and some mid-to-late adolescents appear fully rational. Yet the law may create a bright-line category difference, as it does in the case of capital punishment. No capital killer who committed murder when he or she was sixteen or seventeen years old may be put to death, no matter how rational the adolescent may have been at the time. The law draws such bright lines because sometimes the costs of individualized decision making are too high and society is simply better off with a bright-line rule. This does not mean, however, that the law does not care about the behavioral differences when creating a general rule.

In what types of individual cases can neuroscience help? First, the data must be generally scientifically valid. They have to show precise correlations between brain states or activity and reliable and valid measures of legally relevant behavior, such as rational capacity. Such validity is increased if there is little overlap between the brain and behavior links of the groups being contrasted. In other words, the greater the overlap between the brain activity of people who do and do not meet a legal criterion, the greater will be the difficulty of using the scan of an individual to decide on which side of the line the person falls. And in nearly all cases, overlap will occur. Further, the technique and data must be valid for the individual case in question. For example, suppose the legal question is retrospective, such as determining a criminal defendant’s mental state in the past at the time of the crime. Is a present scan a valid indication of what the defendant’s mental state was during the criminal event?

Assume for the purposes of argument that we can solve both types of validity problems. If the behavioral evidence is clear, the neuroscience will be at most cumulative; it might have particular rhetorical force with a decision maker who is unsophisticated about how fMRI images are generated and the like. These images are not pictures of the brain, despite common belief that they are. Nonetheless, this evidence is superfluous. The expense of neuroimaging techniques and the inability successfully to use them with all potential subjects is reason not to use neuroscience in cases in which the behavior is clear. After all, the behavioral evidence is the most direct and probative evidence of behavioral criteria. Consequently, if we do use neuroimaging and the behavioral evidence and neuroscience evidence conflict, we must believe the behavioral evidence.

For example, if the neuroscientific evidence suggests that a criminal defendant has a rationality defect but the behavioral evidence indicates no defect whatsoever, we should conclude that the neuroscientific evidence is invalid in this case. Actions speak louder than images. Consider the following analogy. If a person does not complain of lower back pain or reduced mobility, we can safely conclude that she has no clinically significant lower back problem, even if an MRI of the spine shows substantial abnormalities. And, if the person shows clear signs of pain and reduced mobility, a problem exists even if the spine looks clean. Likewise, if the result of an IQ test does not accord with the subject’s behavior, believe the behavior.

Here is an example from my own experience as a consultant forensic psychologist in a criminal case in which the defendant claimed that she was too unintelligent to be able to form the mental states required by the definition of the offense. She had taken apparently valid IQ tests indicating that her IQ was in the middle 60s—what is usually termed “mild retardation”—and no one could determine whether she was faking. My intervention was simple. I asked whether she had ever applied for a job for which she had to take some kind of screening test? Did she have kids in school, and if so, had she attended parent/teacher conferences? After all, teachers are really good at evaluating intelligence. The real-world data were collected and demonstrated without question that the defendant had an intelligence far above average.

To take a final example, suppose you were concerned with racial discrimination on the job. Research by Mahzarin Banaji, Elizabeth Phelps, and others has found, roughly speaking, that peoples’ brain activity differentially responds to faces depending on whether the face presented is the same race or a different race from the subject. Should we assume a person is a racist or wrongly discriminates because his or her brain activates differentially? Suppose she has never expressed racist attitudes and her behavioral history shows that she always behaves equitably in the real world. Is the person a racist? Or, at least, for legal purposes, should we care about the differential brain activity?

What is the role of neuroevidence in cases in which the behavioral evidence is unclear or ambiguous? In such cases, valid neural markers and proxies may be extremely helpful evidence for determining whether a legal criterion is met. Neural indicators will rarely be dispositive because they will not be perfect markers, but they might genuinely be probative. On the other hand, the sensitivity or specificity of such markers might not be that high for specific legal criteria. If so, caution is warranted.

Now reconsider the case of the man who strangled his wife to death and threw her body out the window. He had a clear abnormality—a large benign subarachnoid cyst pressing on his frontal cortex—that was present at the time of the crime. Such a finding would certainly not be inconsistent with a rationality defect. But there was no hint that he suffered from a major mental disorder or had any substantial rationality defect either before or after the time of the crime. Some evidence existed that perhaps he had some impulse control problems, but nothing that had ever seriously interfered with his life or caused troubles with the law. Mild impulse control problems are not an excusing condition in any case. Sometimes otherwise law-abiding, rational, and responsible people just “lose” it. If the behavioral history had been more problematic, however, then the potential effect of the cyst might well have caused us more readily to believe that he did suffer from a rationality defect. Similarly, in a case in which intelligence is clearly relevant, if the real-world evidence about intelligence is ambiguous, scientific tests of intelligence, whether psychological or neuroscientific, would surely be helpful.


I have so far been arguing for a cautious, somewhat deflationary stance toward the potential of neuroscience to help us decide general and specific legal issues, but I do not mean to suggest I am a radical skeptic, cynic, or the like. I am not. I do not know what science is going to discover tomorrow. In the future we might well find grounds for greater optimism about broader legal relevance. But we have to be extraordinary sensitive to the limits of what neuroscience can contribute to the law at present.

How should the law proceed? What is the danger of images? The power of images to persuade might be greater than their legal validity warrants. First, images might not be legally relevant at all. We must always carefully ask what precise legal question is under consideration and then ask whether the image or any other neuroscience (or other type of) evidence actually helps us answer this precise question. The image might indicate something interesting, and it might be a vivid, compelling representation, but does it precisely answer our legal question?

Second, once naive subjects, such as average legislators, judges, and jurors, see images of the brain that appear correlated to the behavior in question, they tend to fall into the trap that I call the “lure of mechanism” or to make the fundamental psycholegal error discussed previously. That is, they tend to believe that causation is an excuse, especially if the brain seems to play a causal role. In a wonderful recent study (Knutson et al. 2007), researchers were able to predict with astonishing accuracy, depending on what part of the brain was active, whether the subject would or would not make a choice to buy a consumer item. The title of John Tierney’s article reporting on the study in the New York Times—an excellent example of an educated layperson’s response— asked, “The Voices in My Head Say ‘Buy It!’ Why Argue?” Tierney concluded, “You might remove the pleasure of shopping by somehow dulling the brain’s dopamine receptors . . . but try getting anyone to stay on that medication. Better the occasional jolt of pain. Charge it to the insula.” (Tierney 2007). Note the implication of mechanism: When you shop, you are not an acting agent but are at the mercy of your brain anatomy and physiology. You, the acting agent, the shopper, did not decide whether to buy. Your brain did. We are just brains in a mall. But we must resist the lure of mechanism. Brains do not shop; people do.

As a result, should we exclude imaging evidence from the courtroom, or should we, as we commonly do in the law, admit the evidence and trust cross-examination to expose its strengths and weaknesses? In other words, is the proper question the weight of such evidence or whether it should be admitted at all? The answer should depend on the relevance and strength of the science. If the legal relevance of the science is established and the science is quite good, my preference would be to admit the evidence and let the experts dispute its worth before the neutral adjudicator, the judge or the jury. But two criteria must be met first: The science must be both legally relevant and sound.


1. The title of this paper is a precise copy of the title of an article by Apoorva Mandavilli that appeared in Nature in 2006.

2. What follows, in which I draw a parallel between the use of neuroscience for legal purposes and the development of cognitive neuroscience itself, borrows from and liberally paraphrases an excellent article by Hatfield (2000). What I will suggest is not meant to be critical or dismissive of neuroscience or of any other science. Indeed, I firmly believe that most neuroscience is genuinely excellent science. Nonetheless, much as legally relevant neuroscience must begin with identification of the behavior that is normatively relevant, so psychology does and conceptually must precede neuroscience.


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