In June 2024, Massachusetts General Hospital’s Center for Law, Brain & Behavior (CLBB) at Harvard Medical School launched its NeuroLaw Library. Organized into five modules to be fully released in the next two years, this pioneering resource will cover a wide range of topics, from the brains of juvenile justice to elder fraud prevention; from trauma, memory, and asylum to addiction and sentencing reform.
The emerging field of neuroscientific inquiry has long been contributing to criminal law: a well-known example is memory, for which studies have revealed that, unlike a video recording, it is reconstructed every time it is recalled, thus prone to distortion for not only witnesses but judges and jurors, affecting trial outcomes in unintended ways (Lacy & Stark, 2013; Schacter & Loftus, 2013). In recent years, neuroscience has increasingly influenced criminal law. For instance, in an analysis of criminal judicial opinions in the US between 2005 and 2012, Farahany (2016) found that “about 100 judicial opinions per year discussing neurobiological evidence in criminal law in 2005 climbed to around 250–300 opinions in 2012.” Such evidence, from medical records of head or brain trauma to neuropsychological tests and brain scanning, is used in “at least 5-6% of murder trials” and “1-4 % of other felony offenses” in the US in the study period. For example, in People v. Ruiz (2010), the defendant, charged with murder, was deemed “incompetent to stand trial” due to a serious developmental neurological disorder that limited his language abilities. In Arseneau v. State (2012), the defendant was deemed “incompetent to plead guilty” given mental health and cognitive problems leaving the defendant with issues of memory and comprehension. In Curtis v. State (2011), the appellate court overturned an earlier ruling by lower courts, determining that the defendant was “not guilty by reason of insanity” at the time of murder. In Dietrich v. Ryan (2010), the appellate court ruled that the defense attorney provided “ineffective assistance of counsel” for failing to examine the defendant’s brain damage.
It is unsurprising why the incorporation of neuroscientific evidence into criminal court cases is rising in prevalence. Defense attorneys often try to use neurobiological evidence through expert testimony to challenge the mental competency of the defendant, or the capacity for rational thought (Farahany, 2016). When assessing a defendant’s responsibility or guilt in criminal trials, neuroscientific evidence of intention, conscious voluntariness, and impulsive versus premeditated mental states could theoretically address the foundational concept of mens rea, or a guilty mind. In a consequential article, Greene and Cohen (2004) argued that neuroscientific knowledge might challenge the long-standing legal conception of free will, which is based on the “illusion” of “folk psychology.” Indeed, our seemingly compelling, widely held intuitions about the inner workings of the mind have been repeatedly demonstrated to be grossly inaccurate upon empirical scrutiny, a phenomenon which cognitive scientists called “instinct blindness” (Cosmides and Tooby, 1994).
Neuroscience had its most significant impact in the realm of juvenile criminal justice, when the US Supreme Court cited neuroscientific research findings, during oral arguments and later in its opinions, to support its rulings to abolish the death penalty (Roper v. Simmons, 2005) and deem unconstitutional life imprisonment without parole (Graham v. Florida, 2010 and Miller v. Alabama/Jackson v. Hobbs, 2012) for teenagers younger than 18 years old, who are convicted of homicide or non-homicide crimes (Steinberg, 2013). By the time of the rulings, there is already consensus among the neuroscience community that the asymmetry in adolescent brain development, in which the “socioemotional, incentive-processing system” is stronger than the “cognitive control system,” leads to heightened “risk-taking” and “sensation seeking” behaviors and related criminal offenses among teenagers, compared to other age groups (Steinberg, 2013).
In fact, the increasing volume of such neuroscience research has seen a proportional rise in its being featured in the Supreme Court decisions, which posited that the “immaturity in higher-order executive functions such as impulse control, planning ahead and risk avoidance” in the teenage brain makes the juvenile offender less “culpable” and “blameworthy” than an adult in the same circumstances, thus a sentencing of equal severity is unfair by “penal proportionality analysis” and “violates the Eighth Amendment of the US Constitution, which prohibits ‘cruel and unusual’ punishment” (Steinberg, 2013).
Neuroimaging techniques, among them the most popular being functional magnetic resonance imaging (fMRI), can potentially accomplish brain/mind reading—or the decoding and recreating of information and thoughts in the brain just by feeding fMRI signals into computer models—which could have groundbreaking implications for validating the truthfulness of defendants’ responses during interrogation or witness testimony, should these technologies become mature (see Cox and Savoy, 2003; Norman et al., 2006). One might expect that the “seductive allure of neuroscientific explanation” might bias judges and juries to be persuaded more than other types of evidence (Weisberg et al., 2008). Nonetheless, while some studies have shown that using neurobiological evidence for psychopathy can shorten sentencing (e.g. Aspinwall, Brown & Tabery, 2012), the reality is that a majority of attempts at using neurobiological evidence are either inadmissible and excluded from trial proceedings, or fail to compete with other evidence to mitigate sentencing, let alone reversals or modifications of court decisions by appeal—which have a success rate of less than 20% (Farahany, 2016). Interestingly, mock jury experiments have similarly found that the presentation of neuroimaging evidence had little effect on jurors’ decisions in verdict and sentencing (e.g. Schweitzer et al., 2011). Why, then, does there seem to exist a disconnect between the promise of neuroscience advancements and their utility in criminal law?
To address this dilemma, it is imperative to discuss some fundamental limitations of brain scanning research that warrant caution when assessing how their presentation as evidence in court should apply to legal reasoning. There remains significant privacy concerns: with wearable technologies that collect data of brain activity likely becoming more popularized in the near future, users’ rights to protecting sensitive personal information might be violated if they cannot consent to the use of such data in contexts outside of the products and services themselves. It is critical, also, to preface with the fact that fMRI measures oxygenated blood flow to different brain areas to infer brain activity indirectly. A telling example is the proposal of fMRI’s potential for lie detection, since different studies found similar “activation” patterns in specific brain regions when comparing the averaged differences in data from participants telling the truth versus a lie. Yet these studies suffered from methodological issues such as lack of replicability, small sample size and diversity, and concerns of ecological validity—whether the effects observed from artificial lab tasks would be consistent in real-world situations (Greely and Illes, 2007).
Similarly, a more recent meta-analysis identified several confounding variables suggesting how the supposed “activation” of brain regions reported might not actually represent the act of deception, but general cognitive processes (such as memory and attention) involved in deception itself, among other aspects of the experimental tasks (Farah et al., 2014). In fact, this is a general constraint of fMRI: it remains extremely challenging if not outright impossible to establish causality between the cognitive process under study (in this case, telling a lie) and the “activation” patterns found by fMRI, since these patterns might only be revealing correlations that can include other related processes, or epiphenomena.
Another major issue with applying neuroscientific research to criminal trials is the group-to-individual problem, also known as G2i (Faigman, Monahan & Slobogin, 2014). To extend the example of lie detection, even supposing that researchers can somehow establish the brain regions and firing patterns involved specifically in lying, these results would be averages from samples of the general population, which might not be applicable to the individual defendant. That is, despite that neuroimaging was performed on the defendant, conclusions that connect such data to findings from scientific literature might not be valid. One can picture bell curves representing normal distributions: what academic research summarizes are the central portions of such distributions, which in representative and unbiased samples should theoretically reflect the population for a given neurological measure. However, it is not hard to imagine how the defendant’s data point might not lie within these ranges, especially if their individual circumstances and characteristics do not match those of the participants in the samples of studies from which the evidence was derived. Hence, our judicial system should be vigilant and give less weight to evidence that are not specific to medical diagnoses of the specific defendant standing trial, especially mere generalizations of supposed correlations between brain activity patterns and behaviors in the general population.
Neuroscience might have revolutionized our conceptions of choice and responsibility in mass media and popular culture, but there are considerable hurdles that must be overcome before neuroscience will enjoy a similar impact on criminal law. Before then, there is an urgent need for legal stakeholders to equip themselves with an informed appreciation of the nuances that underlie neuroscientific discoveries, so as to find a balance between caution and receptiveness to new knowledge that are bound to be generated in the years to come. Legal professionals, judges, and juries should be given basic training so they can assess neuroscientific evidence in criminal proceedings through an objective lens, mitigating the effects of personal biases. Educational institutions, nonprofits, and think tanks should spearhead more collaborative and interdisciplinary efforts between cognitive science and law in academia and policy discussions, such that more resources can be directed at addressing the challenges of applying our knowledge on human cognition in the realm of criminal legal reasoning.