The Impact of Neuroscience Evidence on the Criminal Law
The President’s Council on Bioethics
“Here was this nice color image we could enlarge, that the medical expert could point to…it documented that this guy had a rotten spot in his brain. The jury glommed onto that.”
~Chris Plourd (defense attorney)
“In approaching human behavior, science and ethics/law have different objectives and interests: science seeks to understand it, ethics seeks to judge it wisely. Law, the embodiment and teacher of many of the community’s shared moral practices and norms, seeks to protect the community against dangerous or unacceptable behavior by judging misconduct and punishing offenders.”
“In previous generations, people looked to inheritance (genetics), anatomic features (phrenology), a history of emotional trauma or unresolved psychic conflicts (psychoanalysis), or socioeconomic deprivation (sociology and economics) to explain why some people commit crimes and others do not. Today and tomorrow, it seems, people will look increasingly to the brain (neuroscience).”
The Two Chief Aims of the Criminal Law: Determination of Guilt/Culpability and Punishment
Guilt and Mens Rea: The Causal and Moral Role of the Guilty Mind
The Model Penal Code: (a) Negligently, (b) Recklessly, (c) Knowingly, and (d) Purposely
Three Degrees of Homicide (same actus reus but different mens rea): (a) Murder (knowingly or purposely), (b) manslaughter (recklessly), and (c) negligent homicide.
Culpability and Excuse: “The law excuses criminal conduct if there are circumstances that negate the moral blameworthiness of the actor.”
“To blame a person is to express moral criticism, and if the person’s action does not deserve criticism, blaming him is a kind of falsehood, and is, to the extent the person is injured by being blamed, unjust to him. This lies behind the law’s excuses.” ~ Sanford Kadish
The Affirmative Defense of Insanity
Insanity Defenses: (a) M’Naghten Rule—“at the time of the committing of 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, he did not know he was doing what was wrong”, (b) The Irresistible Impulse test—a defendant was not responsible/culpable if he did not have the ability to control his behavior, (c) The Durham Rule—“an accused is not criminally responsible if his unlawful act was the product of a mental disease or defect”, and (d) ALI’s MPC Rule—“a person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity to either appreciate the criminality of his conduct or to conform his conduct to the requirements of the law”.
Sentencing and Mitigating vs. Aggravating Circumstances
The Awkward Balance: Future Dangerousness and Violence Impulsivity
Scientific Evidence, Daubert, and the Judge as Gatekeeper (excerpt from a forthcoming paper of mine):
“Whether used to read minds, assess responsibility, or predict future violence, neuroscientific findings will need to meet legal standards of evidence in order to be accepted into a certain legal context. These standards vary. Evidentiary standards are relatively loose in sentencing and parole hearings, where neuroprediction is usually proposed for use, but much stricter standards apply in civil and criminal trials (especially jury trials), where proponents want to use neuroscience to read minds and assess responsibility. Skeptics often argue that neuroscientific evidence cannot meet these stricter standards for use in trials. To see why, we need to understand those standards.
In the landmark decision in Daubert v. Merrell Dow Pharmaceuticals, the U. S. Supreme Court held that federal judges have a duty to “ensure that any and all scientific testimony or evidence admitted [into a trial] is not only relevant, but reliable.” The Court then provided a list of criteria to assist judges in making determinations concerning the reliability of scientific evidence:
- Has the technique been subjected to falsification and refutation via experimentation?
- Has the technique been subjected to peer review and publication?
- What is the known or potential rate of error?
- Has the technique been generally accepted within the relevant scientific community?
The young age of many neuroscientific findings makes the last two tests difficult to pass. In addition, judges also need to determine whether the expert testimony or evidence applies to the particular case: “Faced with a proffer of expert scientific testimony … the trial judge … must make a preliminary assessment of whether the testimony's underlying reasoning or methodology is scientifically valid and properly can be applied to the facts at issue….” This requirement introduces new difficulties, both because neuroscientific results are often about groups instead of individuals and also because neuroscientific research is often done in lab settings that are very different from the contexts of legal trials.
Additionally, judges were also directed to consider the potential prejudicial impact of scientific evidence in trials. Writing for the majority, Justice Blackmun wrote:
[Federal Rule of Evidence] 403 permits the exclusion of relevant evidence “if its probative value is substantially outweighed by the danger of unfair prejudice…or misleading the jury…” Judge Weinstein has explained: “Expert evidence can be both powerful and quite misleading because of the difficulty in evaluating it. Because of this risk, the judge in weighing possible prejudice against probative force under Rule 403…exercises more control over experts than over lay witnesses.”
In the case of neuroscientific evidence, this danger of prejudicial impact may be especially pressing because of the high regard in which neuroscience is held.
Some researchers have found that exposing people to neuroscientific evidence may have a tendency to unduly influence their decision making. For instance, Weisberg et al. (2008) exposed subjects to good and bad explanations with and without “neurobabble” — i.e., nonsensical or irrelevant brain information that consisted of purposely “circular restatements of the phenomenon, hence, not explanatory” (Weisberg et al. 2008, 471). Their main finding was that despite the fact that the neurobabble added nothing of explanatory value, subjects nevertheless favored the explanations that were supplemented with neurobabble. This result has been supported by other studies (Gurley & Marcus 2008; McCabe & Castell 2008). More recently, however, McCabe et al. (2011) and Schweitzer et al. (2011) suggest that brain images have less impact in legal contexts than elsewhere. Thus, the prejudicial impact of neuroscientific evidence remains an open (and presumably scientific) question.
Insofar as neuroscientific evidence really does have this kind of prejudicial effect, the legal system needs to ensure that legal decision makers do not confer greater weight to neuroevidence than is warranted. But until we know more about how neuroevidence is likely to be interpreted and understood by jurors and judges, we will not be in a position to make informed decisions concerning whether (or when) neuroevidence ought to be used for purposes of the law. Absent strong evidence that neuroevidence has prejudicial impact that substantially outweighs its potential probative value, these predictions will presumably be treated by the courts on par with more traditional forms of evidence.”
Negation of Mens Rea: What kind of neuroevidence should count? What does the neuroevidence add above and beyond behavioral evidence?
Determination of Guilt and the Excuse Defense of Insanity: Hinckley, CT Scans, Brain Atrophy, and Civil Commitment. Question: Here again, what did the neuroevidence add to Hinckley’s defense?
People v. Weinstein, PET Scans, and Brain Abnormalities: Prosecution offers a Plea Bargain
Sentencing and Brain Imaging: The Sword of Justice Cuts both Ways
“The determination of moral responsibility is an integral function of the criminal law, both at the guilt and the punishment phases. Science-based testimony (usually psychiatric) has already established a legitimate place in both phases. Neuroimaging technology, still in its infancy, has already had a modest impact on this process. At the guilt phase, neuroimaging evidence has been marshaled in support of claims of insufficient mens rea and as an adjunct to the insanity defense. At the punishment phase, neuroimaging evidence has been introduced to support claims of mitigation.”
 Id. at 595.
 See Nadelhoffer et al. (forthcoming) for the first studies that specifically look at the impact that neuroprediction has on potential legal decision makers.