By Stephen J. Morse, JD, PhD
Stephen J. Morse is Ferdinand Wakeman Hubbell Professor of Law, Professor of Psychology and Law in Psychiatry, and Associate Director of the Center for Neuroscience & Society at the University of Pennsylvania. He is also a board-certified forensic psychologist. His areas of expertise are criminal law, mental health law, and law and neuroscience. He is the recipient of the American Psychiatric Association’s 2014 Isaac Ray Award for distinguished contributions to forensic psychiatry and the psychiatric aspects of neuroscience. He is also a member of the AJOB Neuroscience editorial board.
What is the relevance to the law’s behavioral criteria of the “new” cognitive, affective and social neuroscience that has been fueled by non-invasive techniques for studying the brain? By behavioral criteria, I mean those that require evaluation of the subject’s acts and mental states. For example, did a defendant charged with homicide kill the victim intentionally? Brain imaging has always been admissible to answer questions about brain injuries and lesions that are medically well-characterized. In such cases, the image is directly relevant to the question of whether the plaintiff had an injury or lesion. In the behavioral cases, however, the imaging will be inferentially relevant and inherently more problematic.
The two basic questions about scientific or technical expert testimony are whether the testimony is scientifically or technically valid and even if so, whether it is legally relevant. In the rest of this blog, I will assume that any proffered expert testimony based on scanning is scientifically or technically valid. Also, I will use examples from the criminal law, but the analysis generalizes to behavioral criteria in the civil law, such as whether a person was competent to contract.
In short, the question is, “How, precisely, does the proffered scan or data based on scanning answer the specific legal question it supposedly helps answer?” I conclude that, at present, brain imaging has little relevance to behavioral legal criteria. The primary exception is cases in which the subject has a well-characterized brain abnormality, such as epilepsy, that may be probative of a legal question such as whether a criminal defendant’s harmful bodily movements were “acts” as the criminal law defines action.
The criteria for criminal responsibility are completely folk psychological—actions and mental states. Neuroscience is a completely mechanistic science. Neurons, neural networks, and the connectome do not have mental states such as intentions, they do not have a sense of past, present, and future, and they do not have aspirations. These are properties of persons. Is the apparent chasm between those two types of discourse bridgeable? Neuroscience eschews folk-psychological concepts and discourse (although, amusingly, much neuroscientific writing sounds very dualistic by suggesting that regions of the brain do things and that the brain and the self are often in a struggle). Thus, the task of translation from the science to the law’s folk psychological criteria will be hard.
The brain does enable the mind (even if we do not know how this occurs). Facts we learn about brains in general or about a specific brain could in principle provide useful information about mental states and about human capacities in general and in specific cases. The question is whether some concededly valid neuroscience is legally relevant because it makes a proposition about responsibility more or less likely to be true. Biological variables, including abnormal biological variables, do not per se answer any legal question because the law’s criteria are not biological. Any legal criterion must be established independently, and biological evidence must be translated into the criminal law’s folk-psychological criteria. That is, the advocate for using the data must be able to explain precisely how the neurodata bear on whether the agent acted, formed a required mental state, or met the criteria for an excusing or mitigating condition. If the evidence is not directly relevant, the advocate should be able to explain the chain of inference from the indirect evidence to the law’s criteria. At present, few data exist that could be the basis of such an inferential chain of reasoning (Morse & Newsome, 2013), but neuroscience is advancing so rapidly that such data may exist in the near or medium term.
A pressing concern is the value-added of imaging. A scan is relatively expensive and somewhat time-consuming. It thus has the potential for waste and delay unless there is genuine value-added. More important, legally relevant neuroimages must be based on good prior behavioral science that identifies clearly the behavior to which the brain structure or function will be correlated. This raises the problem of cumulation, the danger of unnecessary additional evidence that clutters the courts. For example, the law has treated adolescents differently from adults for centuries based on undoubted average behavioral differences between them. What does scanning data about incomplete brain maturity among adolescents add to what we already knew beyond some potentially causal information? It is unsurprising in light of the behavioral differences that there are brain differences, but would we believe adolescents are not behaviorally different if the current brain imaging data did not show a difference?
In individual cases where the behavior is clear, the imaging data will be cumulative and unnecessary. But, might not neuroscience be especially helpful in cases in which the behavioral evidence is unclear? The answer in principle is that of course it would be helpful, but, as a practical matter it will not be because the neurodata is based on correlations with clear behavioral data, a problem I call the “clear cut” issue. Where the behavior is unclear, the neurodata will not be sufficiently sensitive to help resolve the behavioral issue even if the neurodata can distinguish the already behaviorally clear cases.
The generally pessimistic conclusions I have reached concerning the relevance of imaging to behavioral legal criteria is unsurprising. Cognitive, affective, and social neuroscience, the sub-disciplines most relevant to law, are in their infancy and they work on one of the hardest problems in science—the relationship of the brain to mental states and action. Most of what we know generally is correlational and coarse rather than causal and fine-grained (Miller, 2010). Replications are few, so the data-base necessary to reach firm conclusions simply does not exist. These problems may be substantially ameliorated by advances in neuroscience.
Actions almost always speak louder than images. If the finding of a scan is contradicted by actual behavioral evidence, then we must believe the behavioral evidence because it is more direct and probative of the law’s behavioral criteria. For example, if an agent behaves rationally in a wide variety of circumstances, the agent is rational even if his or her brain appears structurally or functionally abnormal. In contrast, if the agent is clearly psychotic, then a potentially legally-relevant rationality problem exists even if the agent’s brain looks entirely normal.
If a biomarker were virtually perfectly correlated with a legal criterion and it was less expensive to obtain than behavioral data, the biological variable might be a good proxy for the legal criterion. But this would be possible only with clear, legal rules and not with vaguer standards, such as whether a reasonable person would be aware of a particular circumstance. The latter have an inevitable normative component for the decision maker to assess. Moreover, such markers are beyond present neuroscientific expertise.
I believe that many of the claims for the relevance of neuroscience are best characterized as “rhetorically relevant” than genuinely relevant. For example, advocates in capital punishment proceedings hope that the fetching images produced by “real” neuroscience will be more persuasive to decision makers than evidence provided by apparently more suspect social and behavioral science, even if the advocate cannot say precisely how the neuroscience bears on a genuinely mitigating or aggravating condition. Having a brain lesion or injury is not a mitigating or aggravating condition per se. The actual relevance of such brain abnormality evidence therefore requires an account of why the brain evidence makes it more likely that a genuine legally-relevant condition obtains.
There are promising, potentially legally relevant advances in neuroscience, such as an objective neural measure for pain, but for the most part, neuroscience is not yet ready for prime time in the courtroom.
Miller, G. 2010. Mistreating psychology in the decades of the brain. Perspectives on Psychological Science 5(6): 716-743.
Morse, S., and B. Newsome. 2013. Criminal responsibility, competence and prediction. In Primer on criminal law and neuroscience, ed. S. Morse and A. L. Roskies, 150-178. Oxford: Oxford University Press.
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Morse, S. (2014). Brain Imaging in the Courtroom: The Quest for Legal Relevance. The Neuroethics Blog. Retrieved on , from http://www.theneuroethicsblog.com/2014/08/brain-imaging-in-courtroom-quest-for.html