Psychopathic Brains on Trial

aharoni vincentEyal Aharoni, Dept of Psychology, Georgia State University & Nicole A Vincent, Dept of Philosophy, Georgia State University

October 2016 – The law is obsessed with emotions. For instance, in criminal cases, a great deal might rest on whether the defendant was consumed by jealousy just before the commission of the crime, whether he feared for his life, or whether he felt remorseful after the crime was committed. Concern also surrounds the emotions of those making legal decisions, such as whether jurors are likely to be disturbed by gory images, or whether some judges are more empathetic than others.  In search of deeper insight into the emotional life of legal actors, legal systems increasingly turn to recent discoveries, techniques, and technologies from the neurosciences.

A greater understanding of the brain basis of emotion could potentially be relevant to many branches of the law including tort law, medical law, policing, and criminal litigation. However, not all neuroscientific findings on emotion are relevant to, or ready for use in, legal settings. Therefore, to understand how best to integrate the descriptive knowledge of the neurosciences with the normative challenges and duties of the legal system, a highly interdisciplinary effort is required. This interdisciplinary effort has led to the emerging field of neurolaw.

In this paper, we aim to contribute to the scholarship on emotion in neurolaw by critically evaluating the degree to which neuroscientific research on emotion can inform legal decision making in one particular context, that of psychopathy and criminal responsibility. However, in order to appreciate what the science of psychopathy can offer to legal decision making, it is important to first understand the specific ways in which scientists define emotion because these definitions often differ from legal ones. Therefore, we begin our discussion with neuroscientific definitions of emotion followed by an examination of how neuroscientific research on psychopathic emotion processing measures up against common criteria for reduced criminal responsibility. We close by discussing some potential caveats in the application of the neuroscience of emotion to legal decision making in the context of psychopathy.

Neuroscientific Understandings of Emotion

The law typically relies on common-sense or folk definitions of emotion. But when asking what the neurosciences bring to bear on our understanding of the role of emotion in law, it is important to recognize that the neurosciences define emotion differently than legal systems do. This is important because if the legal and scientific understanding of emotions is not the same, then this may cause miscommunication between lawyers and scientists, and subsequently undermine the relevance of the science of emotion to legal questions. Neuroscientific definitions of emotion differ from legal definitions in at least three important ways, which we describe below.

Explicit vs. Implicit Emotion

Whereas folk notions of emotion emphasize the phenomenological or “explicit” qualities of emotions, such qualities are neither a necessary nor a sufficient component of neuroscientific conceptualizations of emotions. From a neuroscience perspective, an emotion is a suite of measureable physiological and neurological changes, not all of which are necessarily felt by the subject or recognized as emotion. For example, although we might think that our attitudes toward other social groups are based on a fair, rational, or at least, consistent set of values, prejudicial attitudes can be easily induced outside our awareness through simple emotional manipulations such as recalling a time when you were angry (e.g., DeSteno, Dasgupta, Bartlett, & Cajdric, 2004). So, we do not always have explicit access to emotional states that influence us. Yet, these “implicit” emotions enable neuroscientists to predict and explain changes in the organism’s outward behavior, independently of the felt emotion. This fact raises important questions for the law about an agent’s ability to control behavior that may be influenced by factors outside his/her awareness.

States vs. Traits

Another distinction relevant to the neurobiology of emotion is the concept of mental states versus traits. A mental state is an acute, temporary phenomenon such as a bad mood. The mood might be triggered by an environmental cue such as being mistreated, and may dissipate in a matter of hours or minutes. An emotional trait, in contrast, can be defined as a stable, dispositional character attribute that maintains consistency over long periods, such as when a person is highly empathetic across various situations over time (Davitz, 1969). This distinction between states and traits is relevant to legal inquiry insofar as it reveals something about an actor’s inherent tendency, and perhaps capacity, to behave in a particular socially acceptable or unacceptable way.

Disruptive Events vs. Adaptive Systems

Legal doctrine often characterizes emotions as disruptive and dysfunctional. Many neuroscientists, however, view emotions as helpful biological strategies that evolved to enable organisms achieve their biopsychosocial goals. For example, social emotions like anger, guilt, gratitude, and jealousy are believed to have evolved to solve recurring problems involving social exchange (Tooby & Cosmides, 2008). The variety of goals subserved by adaptive emotion systems can be organized into at least five broad classes: (a) perception: selecting and interpreting external information including others’ mental states, (b) motivation: preparing the organism to engage in a particular kind of action, (c) regulation: exerting inhibitory control over emotional compulsions, (d) communication: signaling one’s needs to others, and (e) calibration: resetting one’s own internal expectations and thresholds for action. This systems approach to emotion is potentially relevant to the law to the extent that the law must assess what individuals (such as a particular defendant) might have perceived during a particular event, what they might have intended, how easy it was for them to control their behavior, whether they are likely to learn from their mistakes, and so on.

In summary, neuroscientific definitions of emotion differ in various ways from folk and legal conceptions. This requires careful analysis of the tacit assumptions surrounding emotion talk in the legal profession and in neuroscience, to avoid misunderstanding. Furthermore, if emotions are part of the implicit biological machinery that generate particular kinds of actions, as neuroscientists believe, then neuroscientific findings presents both an opportunity and burden for legal entities to evaluate when these causes of behavior are relevant to legal decisions such as decisions hinging on assessments of an individual’s perceptions, motivations, capacities, and values.

Implications of Emotion for Criminal Responsibility: Psychopathy as a Case Study

In order to assess how neuroscientific perspectives on emotion could play out in real legal decisionmaking, it is instructive to consider very specific problems in particular sub-areas of the law. Our case study focuses on criminal responsibility in psychopathy. Psychopathy has been described as a personality disorder with a constellation of affective and behavioral characteristics including impulsivity, manipulativeness, and lack of empathy and remorse (Hare & Neumann, 2008). Though they make up less than 1% of the general population, they are disproportionately represented in correctional settings (Hare, Hart, & Harpur, 1991).

Psychopathy is a useful case study because there is a sizeable scientific literature implicating psychopathy as a neurobiological disorder involving aberrant emotional processing, and yet psychopathy is almost never a legitimate defense in a court of law. Clearly, a gap remains between the descriptive scientific results and normative legal criteria for reduced responsibility, but exactly what normative criteria are being used to evaluate the legal status of psychopathy—and whether these criteria are doing justice to the science—is far from clear. Our aim is to elucidate some of these questions by considering how well the neuroscience of psychopathic emotion processing measures against legal standards associated with the insanity defense. Specifically, we will investigate whether psychopathic individuals who commit crimes can justifiably invoke defenses involving impairments in perception, judgment and control. But before doing so, it is important to remind our readers of how our legal system defines crime and responsibility.

Legal definitions of crime and responsibility

Crimes are acts or omissions defined as offenses within the criminal statutes of a given jurisdiction, they are prosecuted by the state and at the state’s discretion, and a finding of criminal guilt may result in the offender’s being punished by the state. Furthermore, criminal offenses are defined by two elements—an “actus reus” and a “mens rea”. In order for a person to be convicted of having committed that specific criminal offense, both elements must typically be proven beyond reasonable doubt. The actus reus element (forbidden act) specifies what a person must have done or failed to do—for example, unlawful killing of a human being, non-consensual sexual intercourse, or failing to come to another person’s aid (the last of these being an example of an omission). And the mens rea (guilty mind) element specifies the degree of intention with which that actus reus must have been committed—for example, on purpose, with knowledge, recklessly, negligently, or in some cases regardless of intention (also known as “strict liability”). Thus, to be guilty of a hate crime, for instance, part of the mental element of that crime must be that it was motivated by hatred—or, at least, the behavior preceding the actus reus must convey the appearance of hatred—of a recognized and prohibited sort (e.g. of a racial group) at least in the context where it functions as a motivation for the commission of the prohibited act.

A defendant may escape a finding of criminal guilt (and thus criminal liability) if he or she successfully raises a recognized defense such as any of a number of mental capacity related defenses. Our focus here will be on the insanity defense.

For instance, under the M’Naghten rule for insanity—upon which many Anglo-American jurisdictions’ insanity rules are based—guilt is diminished when “at the time of committing the act, the party accused was laboring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or if he did know it, that he did not know what he was doing was wrong” (M’Naghten 1843). We take the reference to knowing the nature and quality of the act one is doing to be a reference to the capacity for right perception, and the reference to knowing whether what one does is wrong to be a reference to the capacity for right judgment, reason, or rationality. The Irresistible Impulse test, derived from Parsons v State (1887) (for discussion see e.g. Hauer 1944; or Gerber 1975), adds a volitional prong to the M’Naghten defense, allowing for diminished responsibility when defendant’s capacity to control their actions was significantly impaired.

All three prongs—that is, perception, judgment, and control—are mentioned under the Model Penal Code’s formulation (American Law Institute, 1962). There, guilt is said to be diminished if as a result of mental disorder the defendant lacked substantial[1] capacity either to appreciate the wrongfulness of his action (appreciation presumably requires both right perception and the ability to judge or reason correctly about what one is doing) or to conform his conduct to the requirements of law (which we take to be a reference to control). Much of the above thinking about responsibility rests on the idea that responsibility tracks mental capacity. In lay thinking, this is why children, the senile, and the mentally ill are thought to be less than fully responsible for what they do (i.e. because they lack the right kind and/or degree of mental capacity), why adolescents can acquire more and/or greater responsibilities (i.e. because mental capacities develop as children mature), and how responsibility is supposed to be reinstated on recovery from mental illness (i.e. because mental capacities are recovered) (Vincent, 2011).

Given this capacity-centric framing, impaired perception, judgment, or control—as long as it is a consequence of a (sufficiently severe) recognized disease of the mind—may diminish criminal guilt via its impact on actus reus (e.g. like in sleep-walking cases where the lack of consciousness means that the behavior is treated as a form of “automatism” rather than as genuine action, as something that happened to the offender as much as to their victim) or mens rea (like in the insanity defenses briefly discussed above).

Given the above sketch of what crimes are, of the elements of a criminal offense, and of how criminal guilt can be diminished, if it could be shown that certain emotions can undermine (or are needed for) accurate perception, judgment, and control, then the influence of those emotions may have a bearing on a person’s criminal guilt.

A growing body of evidence suggests that individuals with psychopathy exhibit failures in perceptions of emotion, emotion-based judgments, and emotion regulation/control. In what follows, we use the example of scientific studies of psychopathy to demonstrate how scientific evidence of emotional deficits in psychopathic criminal offenders arguably diminishes psychopaths’ criminal guilt by adversely impacting on their mental capacities that are relevant to actus reus and mens rea, and thus to their criminal guilt.  We do this by examining the utility of neuroscientific evidence of emotion dysfunction in psychopathy for addressing legal criteria for diminished mental capacities in perception, judgment, and control.

Emotion and Perception

A substantial body of research suggests that individuals with psychopathy exhibit failures detecting and representing others’ affective states. For example, Blair and colleagues found that psychopathic offenders were less accurate than non-psychopathic offenders at perceiving fearful displays presented facially (Blair et al., 2004a) and vocally (Blair et al., 2002). Biological evidence has demonstrated high convergence with such behavioral findings including evidence that people high in psychopathy show a reduced startle response to emotionally unpleasant images (Patrick et al., 1993) as well as a reduced skin conductance response to distress cues (Blair, 1997). Moreover, functional neuroimaging studies suggest that brain regions that subserve emotional processing, such as the amygdala and ventromedial prefrontal cortex, are less strongly engaged in psychopathic individuals in response to facial displays of emotion (Gordon et al. 2004), emotional pictures (Muller et al. 2003, 2008), and emotional memory tasks (Kiehl et al. 2001; see Blair, 2008). Correspondingly, structural neuroimaging research has found a negative association between psychopathy level and volumetric measures of the amygdala (Tiihonen et al. 2000; Ermer et al. 2012).

Emotion and Judgment

Research in moral reasoning has long supported the view that emotional and instrumental reasoning processes both play active roles in normal moral judgment. While both of these processes are likely to interact in complex ways to produce normal moral judgment, studies suggests that they are at least partly, experimentally dissociable. One such study asked healthy participants undergoing functional brain imaging to make decisions about hypothetical moral dilemmas (e.g., killing an innocent person to save five others) for scenarios that varied in how “up-close and personal” they were (e.g., killing by pulling a lever or pushing a person). The assumption here is that more upclose and personal dilemmas are more emotionally demanding. Unique areas of activation were found for the more personal dilemmas and included regions such as the medial frontal cortex and cingulate gyri (Greene, Sommerville, Nystrom, & Darley, 2001). Furthermore, the introduction of cognitive load during moral judgment tasks in healthy adults has been shown to interfere with instrumental moral judgments but not emotion-driven ones (Greene, Morelli, Lowenberg, Nystrom, & Cohen, 2008).

Research on moral judgment in psychopathy converges with the findings among healthy populations. In similar moral dilemma tasks, participants high in psychopathy are more likely than their low psychopathy counterparts to endorse judgments achieving instrumental as opposed to emotional ends (Bartels & Pizarro, 2011), and they are more likely to recommend punishments based on practical considerations of future dangerousness than emotional considerations of deservingness (Aharoni, Weintraub, and Fridlund, 2007). This judgment pattern parallels that of patients with ventromedial prefrontal cortex damage in similar tasks (Koenigs et al., 2007), lending support to the conclusion that medial frontal regions play a distinctive role in typical, emotionally-driven moral judgment.

Emotion and Control

Behavioral research suggests that individuals with psychopathy have blunted fear conditioning—that is, they have problems inhibiting a tempting action in order to avoid an aversive stimulus. For example, classic research on avoidance learning showed that when psychopathic individuals were tasked to navigate a difficult maze that punished incorrect moves with an electric shock, these participants made significantly more commission errors relative to control subjects (Lykken, 1957; see also Blair et al. 2004b; Hare 1970; Newman 1987; Schmauk 1970). Interestingly, Schachter and Latané (1964) were able to reduce such commission errors in psychopathic individuals by increasing adrenaline concentrations in the bloodstream, suggesting an important role for the physiological stress response in inhibitory processes.

The ability of psychopathic individuals to regulate their impulses has been observed in risky decision making tasks such as the Iowa Gambling Task described above. In a typical task, participants are presented with several decks that, unbeknownst to the participants, differ in their proportion of “good” (rewarding) versus “bad” (punishing) cards. Unlike healthy participants, those high in psychopathy are more likely to persist in drawing from bad decks (van Honk et al. 2002), a pattern that is similar to patients with ventromedial cortex damage (Anderson et al., 1999; Koenigs et al., 2010) and orbitofrontal damage (Yechiam, Busemeyer, Stout, & Bechara, 2005). Given evidence that the healthy frontal cortical areas receive projections from the amygdala and are believed to down-regulate emotional input (Blair, 2008), these results suggest converging evidence that psychopathic individuals have a reduced ability to learn from punishment, and this dysfunction has roots in aberrant emotional processing.

The strong case for emotional dysfunction in psychopathy

Drawing upon the evidence of emotional dysfunction in psychopathic perception, judgment, and control processes, scientists have theorized that psychopathic antisocial behavior is accounted for by impairments to the neurophysiological mechanisms that implement perceptual, cognitive, and volitional mental capacities. For example, according to Blair’s Violence Inhibition Model, a prominent theory of psychopathic dysfunction, individuals with psychopathy may be more susceptible to engaging in violent behavior because they lack some of the physiological and neurobiological equipment that otherwise help to perceive distress (Blair, 1995; Blair, 2007). Perceiving distress is important because it helps us to know when we might be causing someone harm so we can inhibit that behavior. Without this ability, individuals may be less likely to empathize with others because they do not recognize their distress as clearly. Consequently, they may be less likely to inhibit an inappropriate action because they fail to see reason to do so. To summarize this argument, behavioral and neuroscientific evidence appears to converge on the view that psychopathic individuals have diminished capacity to process emotion which plays a crucial role in accurate perception, proper judgment, and adequate control.

A similar position is often echoed in the philosophical literature, much of which is informed by the above-mentioned and related scientific research. For instance, in recent years, the mantra that mental incapacities can excuse criminal behavior has also played a prominent role in what various people have said about the moral and legal responsibility of individuals with psychopathy. Philosophers cite empirical studies which suggest that alongside reason, affect also plays an important role in moral judgment (e.g. see the special issue edited by Gerrans & Kennett, 2006; especially Prinz, 2006), and that psychopathic individuals have deficits in both affective and rational mental capacities (Blair, 2008; Hare & Neumann, 2010; Kennett, 2010). These deficits appear to be congenital—i.e. they have at least a partial genetic and neurophysiological basis (Harenski et al., 2010) for which psychopathic individuals cannot be straight-forwardly blame. As a result, some have argued that psychopathic individuals should be at least partly excused for what they do, or that their sentences should be partly mitigated (Fine & Kennett, 2004; Levy, 2007; Haji, 2010). Those who endorse this mental incapacity account usually characterize psychopathy as a kind of insanity or moral madness, for example, as a deficit, disorder or mental illness/disease. For instance, they talk about psychopathic individuals being significantly less able than non-psychopathic individuals to do certain things which moral agents must be capable of doing, and about them having neurocognitive deficiencies which they compare to blindness and disability. This approach and related terminology depict people high in psychopathy as victims of mental disease, not dissimilar to criminally insane individuals, for example, as patients who labor under the weight of an all-encompassing medical disorder which (by impairing their perception, judgment, or control) is the true cause of their abnormal, harmful, illegal and immoral behavior.

A key point in this view is that if neuroscientific definitions of emotion are correct—if emotions are potentially implicit, goal-directed biological systems with some degree of trait-like stability—then it would be reasonable to suspect that abnormal emotional processing in psychopathic offenders could consistently influence their behavior in a way that is outside of their awareness and control, much like an “incapacity”.

Unanswered Questions in the Application of Neuroscientific Approaches to Psychopathic Emotion in Criminal Law

Despite the growing body of neuroscientific and behavioral evidence we have reported, a diagnosis of psychopathy is virtually never legally excusing. Yet, psychopathy seems to share some common characteristics with other mental disorders that are more widely regarded as reflecting reduced capacity. For example, autism spectrum disorders are characterised in part by a limited ability to represent others’ thoughts and feelings, a finding supported by neuroscientific evidence (e.g., Baron-Cohen et al., 2000; Mason et al., 2007; Kana et al., 2009). Few would object to the claim that autism entails some reduced capacities that should have a legal bearing.

So why do intuitions about the criminal responsibility of psychopathic individuals differ from that of other mental disorders? One possible answer is that despite the evidence that psychopathic individuals show abnormal behavior in laboratory settings, none of these studies demonstrate a true lack of capacity per se. It remains possible that, under the right conditions, psychopathic individuals can perceive harm, judge wrongfulness, and control their behavior to a reasonable degree. Indeed, there is some justification for this view (Maibom, 2008; Borg & Sinnott-Armstrong, 2013). A second possible reason why psychopathy is treated differently from some other mental conditions is that the evidence regarding psychopathic incapacity is simply less complete, and that more research will be needed before psychopathy can be legitimately compared alongside other well-understood conditions. A third possible reason is that we hold psychopathic individuals to a higher standard, perhaps because of our own preconceptions about their capacities. Regardless of which of these explanations is correct, it remains far from clear what scientific criteria should count as evidence of legal incapacity.

Admittedly, scientific observation will never be able to provide a smoking gun for evidence of incapacity because that would require (impossibly) observing the subject’s behavior in all possible circumstances. However, this is not to say that scientific observation is wholly unuseful in such assessments. We know this because scientists frequently make such assessments in clear-cut cases. For example, we can conclude that a person in a vegetative state lacks the capacity to perform arithmetic. Likewise, we can be fairly confident that a person with a severe autism disorder will, on average, be less capable of understanding others’ intentions. Such conclusions rely at least on implicit if not explicit criteria for capacity, criteria which are informed by empirical observation. This fact assures us that, even without a smoking gun, the prospect of developing criteria for defining certain kinds of capacities among psychopathic individuals may be both valuable and empirically tractable.

In order for the neurosciences to become more useful to the law, they must overcome some important limitations. The first and arguably most compelling is the necessity to develop a ‘translation manual’. Given the differences we have discussed earlier concerning what legal theorists and neuroscientists take emotions to be, cross-purpose talk is inevitable unless major efforts are made to clarify what the various parties “mean” by emotion, and how scientific findings map onto the legal framework.

Once we bar the possibility of terminological misunderstandings, progress will become easier. But we must be clear about what sorts of contributions the neurosciences can offer. For example, a major responsibility of the law is to evaluate past mental and motivational states of individuals, such as whether a defendant feared for his life on a particular evening last year. At present, the neurosciences are not well-equipped to answer retrospective questions about fleeting mental states and should not be used in this way.

On the other hand, neuroscience can inform other types of inquiries, such as questions that rely on stable, group-level data, for example, if it is known that most people with a particular brain disease lack the capacity to regulate their emotions in the way that a healthy, reasonable person would. If the defendant is a member of this population (i.e., carries the same diagnosis), then a strong case can be made the the defendant, too, has difficulty regulating his emotions. Such inquiries can be relevant to legal decision making as long as we have cross-validated ways (e.g., both neurobiological and clinical) of knowing whether the individual in question is a member of that group.

In some cases, neuroscientific research could become more helpful to the law if it specifically targeted legal concerns. For example, in legal settings the question is often not whether or not the defendant had a certain emotion, but why they failed to have a certain emotion given that they had the capacity for it. For instance, on the assumption that the defendant has the capacity for empathy, a judge may ask why  he or she didn’t exercise it when seeing the victim’s cash sticking out of her purse? In other words, why did the defendant’s immediate desire for money override his internal value to do no harm when these two goals were placed in conflict? If neuroscience research is to become more useful to the law, it needs to do more to  address these complex questions about motivational conflict.


This paper has set out to examine issues in the application of neuroscience to questions of emotion in legal decision making. We argued that before the neuroscience of emotion can be responsibly used in legal settings, it is important to appreciate how neuroscientific definitions of emotion differ from legal ones in terms of their functions, stability, and availability to conscious awareness. Using psychopathy as a  case study, we entertained the argument that to the extent that emotions reflect implicit, goal-directed motivational strategies, how these strategies operate could potentially help inform questions of capacity (and thus, responsibility) by revealing when such strategies are likely to fulfill their aims. We focused on the example of psychopathy because courts remain unmoved by the scientific evidence on psychopathic emotion processing, obviating the need to further specify criteria for responsibility. Yet, many remaining questions must be addressed before our intuitions about responsibility can be formalized into a set a criteria that painlessly integrate scientific knowledge about emotion processing with our ethical and legal standards. Our present purpose is not to advance any substantive normative, legal, or scientific claims, but to provide a potentially useful approach for evaluating scientific questions about emotions and law.


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[1] Another important difference between the Model Penal Code’s formulation and other formulations of the insanity defense is that instead of asking whether the defendant completely lacked the requisite capacities, it acknowledges that one may not completely lack a required capacity but may still be insane on account that their impairment was substantial.

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