Law, responsibility, and the brain

Decision Flexibilities in Autism Spectrum Disorder: An fMRI Study of Moral Dilemmas

People make flexible decisions across a wide range of contexts to resolve social or moral conflicts. Individuals with autism spectrum disorder (ASD) frequently report difficulties in such behaviors, which hinders the flexibility in changing strategies during daily activities or adjustment of perspective during communication. However, the underlying mechanisms of this issue are insufficiently understood. This study aimed to investigate decision flexibility in ASD using a functional magnetic resonance imaging task that involved recognizing and resolving two types of moral dilemmas: cost–benefit analysis (CBA) and mitigating inevitable misconducts (MIM). The CBA session assessed the participants’ pitting of result-oriented outcomes against distressful harmful actions, whereas the MIM session assessed their pitting of the extenuation of a criminal sentence against a sympathetic situation of defendants suffering from violence or disease. The behavioral outcome in CBA-related flexibility was significantly lower in the ASD group compared to that of the typical development group. In the corresponding CBA contrast, activation in the left inferior frontal gyrus was lower in the ASD group. Meanwhile, in the MIM-related flexibility, there were no significant group differences in behavioral outcome or brain activity. Our findings add to our understanding of flexible decision-making in ASD.

From Neuroscience to Law: Bridging the Gap

Since our moral and legal judgments are focused on our decisions and actions, one would expect information about the neural underpinnings of human decision-making and action-production to have a significant bearing on those judgments. However, despite the wealth of empirical data, and the public attention it has attracted in the past few decades, the results of neuroscientific research have had relatively little influence on legal practice. It is here argued that this is due, at least partly, to the discussion on the relationship of the neurosciences and law mixing up a number of separate issues that have different relevance on our moral and legal judgments. The approach here is hierarchical; more and less feasible ways in which neuroscientific data could inform such judgments are separated from each other. The neurosciences and other physical views on human behavior and decision-making do have the potential to have an impact on our legal reasoning. However, this happens in various different ways, and too often appeal to any neural data is assumed to be automatically relevant to shaping our moral and legal judgments. Our physicalist intuitions easily favor neural-level explanations to mental-level ones. But even if you were to subscribe to some reductionist variant of physicalism, it would not follow that all neural data should be automatically relevant to our moral and legal reasoning. However, the neurosciences can give us indirect evidence for reductive physicalism, which can then lead us to challenge the very idea of free will. Such a development can, ultimately, also have repercussions on law and legal practice.

Neuroscience-based Psychiatric Assessments of Criminal Responsibility: Beyond Self-Report?

Many legal systems have an insanity defense, which means that although a person has committed a crime, she is not held criminally responsible for the act. A challenge with regard to these assessments is that forensic psychiatrists have to rely to a considerable extent on the defendant's self-report. Could neuroscience be a way to make these evaluations more objective? The current value of neuroimaging in insanity assessments will be examined. The author argues that neuroscience can be valuable for diagnosing neurological illnesses, rather than psychiatric disorders. Next, he discusses to what extent neurotechnological 'mind reading' techniques, if they would become available in the future, could be useful to get beyond self-report in forensic psychiatry.

The Brain of Dexter Morgan: the Science of Psychopathy in Showtime's Season 8 of Dexter

This article identifies and discusses on the ways in which biological influences to psychopathy are thematically portrayed in the eighth season of Dexter to describe Dexter's psychopathy, particularly focusing on fatalism and the inevitability of succumbing to one's "biological self." This paper, utilizing traditional content analysis, focuses on seven qualitative themes surrounding "biological fatalism" and psychopathy in this final season of Dexter. As lay theories of psychopathy are thought to originate from the media's conceptualization of the disorder, such thematic portrayals serve to potential affect lay understandings of psychopathy and correspondingly, how the disorder is treated and perceived in the criminal justice process as a modern psychopathy-related "CSI Effect." The conclusion focuses on the messages that this final season of Dexter sends to the lay public about the biological influences to psychopathy and how this may create implications for the criminal justice system.

How information about perpetrators' nature and nurture influences assessments of their character, mental states, and deserved punishment

Evidence of perpetrators' biological or situational circumstances has been increasingly brought to bear in courtrooms. Yet, research findings are mixed as to whether this information influences folk evaluations of perpetrators' dispositions, and subsequently, evaluations of their deserved punishments. Previous research has not clearly dissociated the effects of information about perpetrators' genetic endowment versus their environmental circumstances. Additionally, most research has focused exclusively on violations involving extreme physical harm, often using mock capital sentences cases as examples. To address these gaps in the literature, we employed a "switched-at-birth" paradigm to investigate whether positive or negative information about perpetrators' genetic or environmental backgrounds influence evaluations of a perpetrator's mental states, character, and deserved punishment. Across three studies, we varied whether the transgression involved direct harm, an impure act that caused no harm, or a case of moral luck. The results indicate that negative genetic and environmental backgrounds influenced participants' evaluations of perpetrators' intentions, free will, and character, but did not influence participants' punishment decisions. Overall, these results replicate and extend existing findings suggesting that perpetrators' supposed extenuating circumstances may not mitigate the punishment that others assign to them.

Violent and Non-Violent Criminal Behavior among Young Chinese Drug Users: A Mixed Methods Study

Young drug users are found to be increasingly involved in criminal justice issues. This exploratory and descriptive study aims to analyze the criminal behaviors among young Chinese drug users through a mixed methods research design. Quantitative analysis indicates that young drug users with and without a history of criminality show significant differences in terms of several features. Male drug users, particularly, those who are older, with religious beliefs, and initiated into drug use at younger age were most likely to commit crimes. Among drug users with criminal experiences, those who committed crimes prior to drug initiation have a greater likelihood of committing violent crimes. Furthermore, young drug users with severe depression are more likely to commit crimes, especially violent ones. Qualitative analysis further illustrates that young male drug users often get involved in criminal conduct of the youth gang nature with propensity for engaging in violent crimes as compared to their female counterparts who are more likely to turn into drug dealers and traffickers, in addition to engaging in larceny. The research findings are consistent with developmental theories and "victim to offender cycle". Integrated mental health and substance use services are suggested for crime prevention among young Chinese drug users.

Integrating Brain Science and Law: Neuroscientific Evidence and Legal Perspectives on Protecting Individual Liberties

Advances in neuroscientific techniques have found increasingly broader applications, including in legal neuroscience (or “neurolaw”), where experts in the brain sciences are called to testify in the courtroom. But does the incursion of neuroscience into the legal sphere constitute a threat to individual liberties? And what legal protections are there against such threats? In this paper, we outline individual rights as they interact with neuroscientific methods. We then proceed to examine the current uses of neuroscientific evidence, and ultimately determine whether the rights of the individual are endangered by such approaches. Based on our analysis, we conclude that while federal evidence rules constitute a substantial hurdle for the use of neuroscientific evidence, more ethical safeguards are needed to protect against future violations of fundamental rights. Finally, we assert that it will be increasingly imperative for the legal and neuroscientific communities to work together to better define the limits, capabilities, and intended direction of neuroscientific methods applicable for use in law.

Behavioral and neural impairments of frontotemporal dementia: Potential implications for criminal responsibility and sentencing

Individuals in the early stages of the behavioral variant of frontotemporal dementia (bvFTD), a progressive neurodegenerative disorder marked by atrophy to the brain's frontal regions, exhibit severe disturbances to social and moral processing and decision-making after the onset of the disorder. These behavioral impairments, underlain by the neural deficits associated with the disorder, can often lead individuals with bvFTD to criminally offend. As such, behavioral and frontotemporal lobe abnormalities exhibited by offenders with bvFTD potentially represent several complex challenges for the legal system. This paper examines some of the ways in which the behavioral and neural impairments associated with bvFTD may influence issues surrounding the criminal responsibility, specifically legal insanity, and sentencing of offenders with bvFTD in the U.S. legal system. As there is very little literature in these areas concerning bvFTD, the existing academic dialogue on psychopathy, a disorder with similar behavioral symptoms and neural deficits, is used to frame the discussion on these issues.

Just like a circus: the public consumption of sex differences

The study of sex differences is a rich, productive area of neuroscience, yielding findings that inform our understanding of basic biology and hold promise for clinical applications. There is a tremendous, problematic mismatch, however, between the actual implications of this research and what has generally been communicated to the public. The message communicated by the media, popular press, and in some cases researchers is often inaccurate with respect to what can and cannot be concluded from the data. This misrepresentation of findings has led to a crisis in public education and threatens to do the same in public health. Here, I suggest a number of ways that neuroscientists might address this growing problem. First, we should acknowledge that the term 'sex difference' is usually interpreted by the media and the public as evidence for dichotomous categories that do not actually exist. Because data rarely sort so cleanly into sex-specific categories, clearer presentation of the nature and size of sex differences is warranted. The term 'sex effect' may be preferable to 'sex difference' when the effect is not large. Second, factors that covary with sex, particularly experience, should be considered as causes of sex differences before the idea of "hardwiring" is invoked. Finally, we should be more vigilant about how our own findings are conveyed to policymakers and the public and speak out when they are misrepresented.

Opportunities, threats and limitations of neuroscience data in forensic psychiatric evaluation

PURPOSE OF REVIEW

In the last decade, a number of studies have been published to shed light on the interaction between neuroscience and the law, notably on the introduction of neuroscience data in forensic psychiatric evaluation (FPE). Even if there is a growing consensus on the relevance of neuroscience in clinical practice, the role of neuroscience in FPE is still controversial.

RECENT FINDINGS

The use of neuroscience data in FPE can support the detection of psychopathological disabilities (e.g. deficit of self-control, aggressiveness) that may be involved in criminal action. Traumatic brain injury-related clinical disorders that may lead to misconduct have a relevant role in the debate. Traditionally, literature refers also to rare and weird cases in which brain tumours, infections and morphological abnormalities were supposed to be significantly associated with disorders leading to criminal action.

SUMMARY

After reviewing recent literature from both legal and neuroscientific perspectives, we consider a broader range of clinical conditions (e.g. disorders of consciousness in sleepwalking, dopamine replacement therapy in Parkinson's disease, misattributions of self in delusional experience) that may have implications in legal settings. Obviously, it would be possible to consider also different clinical conditions. We conclude by suggesting further experimental and theoretical analysis.

Memory disorders in the law courts

This paper reviews the ways in which memory disorders and memory distortions arise in the criminal courts. Amnesia for offences is considered in terms of automatisms, alcohol, and crimes of passion. False memories arise in false confessions, allegations of false memory for child sexual abuse, and, just occasionally, with respect to delusional memories. More generally, memory and neuropsychiatric disorders may have implications at each stage of the legal process (fitness to plead, the insanity defence, cases of automatism, diminished responsibility, and at sentencing). However, patients with memory and neuropsychiatric disorders remain very vulnerable within legal and court processes.

Reviews of functional MRI: the ethical dimensions of methodological critique

Neuroimaging studies involving human subjects raise a range of ethics issues. Many of these issues are heightened in the context of neuroimaging research involving persons with mental health disorders. There has been growing interest in these issues among legal scholars, philosophers, social scientists, and as well as neuroimagers over the last decade. Less clear, however, is the extent to which members of the neuroimaging community are engaged with these issues when they undertake their research and report results. In this study, we analyze the peer-reviewed review literature involving fMRI as applied to the study of mental health disorders. Our hypothesis is that, due to the critical orientation of reviews, and the vulnerability of mental health population, the penetrance of neuroethics will be higher in the review literature in this area than it is in the primary fMRI research literature more generally. We find that while authors of reviews do focus a great deal of attention on the methodological limitations of the studies they discussed, contrary to our hypothesis, they do not frame concerns in ethical terms despite their ethical significance. We argue that an ethics lens on such discussion would increase the knowledge-value of this scholarly work.

Brain imaging analysis can identify participants under regular mental training

Multivariate pattern recognition approaches have become a prominent tool in neuroimaging data analysis. These methods enable the classification of groups of participants (e.g. controls and patients) on the basis of subtly different patterns across the whole brain. This study demonstrates that these methods can be used, in combination with automated morphometric analysis of structural MRI, to determine with great accuracy whether a single subject has been engaged in regular mental training or not. The proposed approach allowed us to identify with 94.87% accuracy (p<0.001) if a given participant is a regular meditator (from a sample of 19 regular meditators and 20 non-meditators). Neuroimaging has been a relevant tool for diagnosing neurological and psychiatric impairments. This study may suggest a novel step forward: the emergence of a new field in brain imaging applications, in which participants could be identified based on their mental experience.

How Predictable are "Spontaneous Decisions" and "Hidden Intentions"? Comparing Classification Results Based on Previous Responses with Multivariate Pattern Analysis of fMRI BOLD Signals

In two replication studies we examined response bias and dependencies in voluntary decisions. We trained a linear classifier to predict “spontaneous decisions” and in the second study “hidden intentions” from responses in preceding trials and achieved comparable prediction accuracies as reported for multivariate pattern classification based on voxel activities in frontopolar cortex. We discuss implications of our findings and suggest ways to improve classification analyses of fMRI BOLD signals that may help to reduce effects of response dependencies between trials.

Brains in context in the neurolaw debate: the examples of free will and "dangerous" brains

Will neuroscience revolutionize forensic practice and our legal institutions? In the debate about the legal implications of brain research, free will and the neural bases of antisocial or criminal behavior are of central importance. By analyzing frequently quoted examples for the unconscious determinants of behavior and antisocial personality changes caused by brain lesions in a wider psychological and social context, the paper argues for a cautious middle position: Evidence for an impending normative "neuro-revolution" is scarce and neuroscience may instead gradually improve legal practice in the long run, particularly where normative questions directly pertain to brain-related questions. In the conclusion the paper raises concerns that applying neuroscience methods about an individual's responsibility or dangerousness is premature at the present time and carries serious individual and societal risks. Putting findings from brain research in wider contexts renders them empirically investigable in a way that does not neglect psychological and social aspects of human mind and behavior.

Impulse control and criminal responsibility: lessons from neuroscience

Almost all of the world's legal systems recognize the "M'Naghten" exception to criminal responsibility: the inability to appreciate the wrongfulness of action. This exception rests on the assumption that punishment is morally justified only if the defendant was able to choose whether to do wrong. Jurists and jurisdictions differ, however, on whether to extend M'Naghten's logic to cases where the defendant understood the wrongfulness of an act but was incapable of resisting an impulse to commit it. In this article I ask whether contemporary neuroscience can help lawmakers to decide whether to adopt or retain this defense, known variously as the "irresistible impulse" defense or the "control" or "volitional" test for insanity. More specifically, I ask firstly, whether it is empirically true that a person can understand the wrongfulness of an act yet be powerless to refrain from committing it; and second (assuming an affirmative answer to the first), whether the law of criminal responsibility can practically accommodate this phenomenon? After canvassing the relevant neuroscientific literature, I conclude that the answer to the first question is "yes." After examining the varied treatment of the defense in the United States and other nations, I also give an affirmative answer to the second question, but only in limited circumstances. In short, the defense of irresistible impulse should be recognized, but only when it can be shown that the defendant experienced a total incapacity to control his or her conduct in the circumstances.

Neuroimage evidence and the insanity defense

The introduction of neuroscientific evidence in criminal trials has given rise to fears that neuroimagery presented by an expert witness might inordinately influence jurors' evaluations of the defendant. In this experiment, a diverse sample of 1,170 community members from throughout the U.S. evaluated a written mock trial in which psychological, neuropsychological, neuroscientific, and neuroimage-based expert evidence was presented in support of a not guilty by reason of insanity (NGRI) defense. No evidence of an independent influence of neuroimagery was found. Overall, neuroscience-based evidence was found to be more persuasive than psychological and anecdotal family history evidence. These effects were consistent across different insanity standards. Despite the non-influence of neuroimagery, however, jurors who were not provided with a neuroimage indicated that they believed neuroimagery would have been the most helpful kind of evidence in their evaluations of the defendant.

Neuroethics and fMRI: mapping a fledgling relationship

Human functional magnetic resonance imaging (fMRI) informs the understanding of the neural basis of mental function and is a key domain of ethical enquiry. It raises questions about the practice and implications of research, and reflexively informs ethics through the empirical investigation of moral judgments. It is at the centre of debate surrounding the importance of neuroscience findings for concepts such as personhood and free will, and the extent of their practical consequences. Here, we map the landscape of fMRI and neuroethics, using citation analysis to uncover salient topics. We find that this landscape is sparsely populated: despite previous calls for debate, there are few articles that discuss both fMRI and ethical, legal, or social implications (ELSI), and even fewer direct citations between the two literatures. Recognizing that practical barriers exist to integrating ELSI discussion into the research literature, we argue nonetheless that the ethical challenges of fMRI, and controversy over its conceptual and practical implications, make this essential.

Neuroimaging and Responsibility Assessments

Could neuroimaging evidence help us to assess the degree of a person's responsibility for a crime which we know that they committed? This essay defends an affirmative answer to this question. A range of standard objections to this high-tech approach to assessing people's responsibility is considered and then set aside, but I also bring to light and then reject a novel objection-an objection which is only encountered when functional (rather than structural) neuroimaging is used to assess people's responsibility.

From moral to legal judgment: the influence of normative context in lawyers and other academics

Various kinds of normative judgments are an integral part of everyday life. We extended the scrutiny of social cognitive neuroscience into the domain of legal decisions, investigating two groups, lawyers and other academics, during moral and legal decision-making. While we found activation of brain areas comprising the so-called 'moral brain' in both conditions, there was stronger activation in the left dorsolateral prefrontal cortex and middle temporal gyrus particularly when subjects made legal decisions, suggesting that these were made in respect to more explicit rules and demanded more complex semantic processing. Comparing both groups, our data show that behaviorally lawyers conceived themselves as emotionally less involved during normative decision-making in general. A group × condition interaction in the dorsal anterior cingulate cortex suggests a modulation of normative decision-making by attention based on subjects' normative expertise.

How neuroscience and behavioral genetics improve psychiatric assessment: report on a violent murder case

Despite the advances in the understanding of neural and genetic foundations of violence, the investigation of the biological bases of a mental disorder is rarely included in psychiatric evaluation of mental insanity. Here we report on a case in which cognitive neuroscience and behavioral genetics methods were applied to a psychiatric forensic evaluation conducted on a young woman, J.F., tried for a violent and impulsive murder. The defendant had a history of multidrug and alcohol abuse and non-forensic clinical evaluation concluded for a diagnosis of borderline personality disorder. We analyzed the defendant's brain structure in order to underlie possible brain structural abnormalities associated with pathological impulsivity. Voxel-based morphometry indexed a reduced gray matter volume in the left prefrontal cortex, in a region specifically associated with response inhibition. Furthermore, J.F.'s DNA was genotyped in order to identify genetic polymorphisms associated with various forms of violence and impulsive behavior. Five polymorphisms that are known to be associated with impulsivity, violence, and other severe psychiatric illnesses were identified in J.F.'s DNA. Taken together, these data provided evidence for the biological correlates of a mental disorder characterized by high impulsivity and aggressive tendencies. Our claim is that the use of neuroscience and behavioral genetics do not change the rationale underlying the determination of criminal liability, which must be based on a causal link between the mental disorder and the crime. Rather, their use is crucial in providing objective data on the biological bases of a defendant's mental disorder.

"Screen and intervene": governing risky brains

This article argues that a new diagram is emerging in the criminal justice system as it encounters developments in the neurosciences. This does not take the form that concerns many "neuroethicists" -- it does not entail a challenge to doctrines of free will and the notion of the autonomous legal subject -- but is developing around the themes of susceptibility, risk, pre-emption and precaution. I term this diagram "screen and intervene" and in this article I attempt to trace out this new configuration and consider some of the consequences.

Affective Neuroscience: Past, Present, and Future

The discipline of affective neuroscience is concerned with the underlying neural substrates of emotion and mood. This review presents an historical overview of the pioneering work in affective neuroscience of James and Lange, Cannon and Bard, and Hess, Papez, and MacLean before summarizing the current state of research on the brain regions identified by these seminal researchers. We also discuss the more recent strides made in the field of affective neuroscience. A final section considers different hypothetical organizations of affective neuroanatomy and highlights future directions for the discipline.

[Forensic psychiatry in the era of neuroscience: present status and outlook for neurobiological research]

Progress in neurobiological research has influenced our view of human beings and the basics of their behavior. Regarding criminal law and forensic psychiatry, established codes of practice are being challenged by neuroscientific research. This article gives an overview of neurobiological findings and methods in the context of forensic psychiatric issues. Empirical approaches to addressing important legal questions are outlined. Principles behind forensic psychiatric expert opinions are given. The effect and future of neuroscientific findings and methods in answering forensic psychiatric questions are discussed. Limitations and legal and ethical requirements are addressed.

Aggression, science, and law: The origins framework. Introduction

Human societies have formalized instincts for compliance with reciprocal altruism in laws that sanction some aggression and not other aggression. Neuroscience makes steady advances toward measurements of various aspects of brain function pertinent to the aggressive behaviors that laws are designed to regulate. Consciousness, free will, rationality, intent, reality testing, empathy, moral reasoning, and capacity for self-control are somewhat subject to empirical assessment. The question becomes: how should law accommodate the wealth of information regarding these elements of mind that the science of aggression increasingly makes available? This essay discusses the evolutionary purpose of aggression, the evolutionary purpose of law, the problematic assumptions of the mens rea doctrine, and the prospects for applying the neuroscience of aggression toward the goal of equal justice for unequal minds. Nine other essays are introduced, demonstrating how each of them fits into the framework of the permanent debate about neuroscience and justice. It is concluded that advances in the science of human aggression will have vital, but biologically limited, impact on the provision of justice.

The development of emotion and empathy skills after childhood brain injury

Lasting socio-emotional behaviour difficulties are common among children who have suffered brain injuries. A proportion of difficulties may be attributed to impaired cognitive and/or executive skills after injury. A recent and rapidly accruing body of literature indicates that deficits in recognizing and responding to the emotions of others are also common. Little is known about the development of these skills after brain injury. In this paper we summarize emotion-processing systems, and review the development of these systems across the span of childhood and adolescence. We describe critical phases in the development of emotion recognition skills and the potential for delayed effects after brain injury in earlier childhood. We argue that it is important to identify the specific nature of deficits in reading and responding to emotions after brain injury, so that assessments and early intervention strategies can be devised.

Infection, incest, and iniquity: investigating the neural correlates of disgust and morality

Disgust, an emotion related to avoiding harmful substances, has been linked to moral judgments in many behavioral studies. However, the fact that participants report feelings of disgust when thinking about feces and a heinous crime does not necessarily indicate that the same mechanisms mediate these reactions. Humans might instead have separate neural and physiological systems guiding aversive behaviors and judgments across different domains. The present interdisciplinary study used functional magnetic resonance imaging (n = 50) and behavioral assessment to investigate the biological homology of pathogen-related and moral disgust. We provide evidence that pathogen-related and sociomoral acts entrain many common as well as unique brain networks. We also investigated whether morality itself is composed of distinct neural and behavioral subdomains. We provide evidence that, despite their tendency to elicit similar ratings of moral wrongness, incestuous and nonsexual immoral acts entrain dramatically separate, while still overlapping, brain networks. These results (i) provide support for the view that the biological response of disgust is intimately tied to immorality, (ii) demonstrate that there are at least three separate domains of disgust, and (iii) suggest strongly that morality, like disgust, is not a unified psychological or neurological phenomenon.

Behavioral measures of impulsivity and the law

The General Theory of Crime proposes that crime is explained by the combination of situational opportunity and lack of self-control. Impulsivity is one of the important components of self-control. Because behavioral measures of impulsivity are becoming more commonly utilized to assess forensic populations, this manuscript provides an overview of three current behavioral measures. In doing so, an example of their application is provided using a group of individuals likely to come into contact with the legal system: adolescents with Conduct Disorder. Earlier age of onset of Conduct Disorder symptoms has been shown to be an important predictor of the persistence of poor outcomes into adulthood, including participation in criminal activities. This study found differential behavioral profiles across distinct measures of impulsivity by those with childhood- versus adolescent-onset Conduct Disorder. Legal implications for defining behavioral deficits using behavioral measures of impulsivity and their current limitations are discussed.

Implications of fMRI and genetics for the law and the routine practice of forensic psychiatry

This review outlines recent neurobiological findings in humans relevant for the practice of law and forensic psychiatry. We focus on offenders with antisocial personality disorder and on sex offenders. In addition, the impact of risk polymorphisms in monoamine oxidase A (MAO-A), previously related to violence in interaction with the environment, on brain structure and function and on personality traits in healthy persons are presented. While increasing knowledge of functional and structural alterations provides a better understanding of the neurobiological underpinnings of delinquent behaviour, antisocial and violent behaviour arises from a complex pattern of biological, psychological, social and situational factors, precluding a stance of simple biological reductionism. Rather, optimal integration of neurobiological findings requires cooperation among many disciplines such as medicine, criminology, sociology, psychology, politics and neuroscience.

Order in spontaneous behavior

Brains are usually described as input/output systems: they transform sensory input into motor output. However, the motor output of brains (behavior) is notoriously variable, even under identical sensory conditions. The question of whether this behavioral variability merely reflects residual deviations due to extrinsic random noise in such otherwise deterministic systems or an intrinsic, adaptive indeterminacy trait is central for the basic understanding of brain function. Instead of random noise, we find a fractal order (resembling Lévy flights) in the temporal structure of spontaneous flight maneuvers in tethered Drosophila fruit flies. Lévy-like probabilistic behavior patterns are evolutionarily conserved, suggesting a general neural mechanism underlying spontaneous behavior. Drosophila can produce these patterns endogenously, without any external cues. The fly's behavior is controlled by brain circuits which operate as a nonlinear system with unstable dynamics far from equilibrium. These findings suggest that both general models of brain function and autonomous agents ought to include biologically relevant nonlinear, endogenous behavior-initiating mechanisms if they strive to realistically simulate biological brains or out-compete other agents.