Brain evidence is playing an increasing role in criminal trials, and new research by Allen and colleagues (2019) suggests that such evidence may have both aggravating and mitigating effects on criminal sentencing. Indeed, legal theorists have previously portrayed physical evidence of brain dysfunction as a double-edged sword: on the one hand, capable of decreasing punitive motivations by minimizing the offender’s perceived responsibility for his transgressions, while, on the other hand, capable of increasing punitive motivations towards the offender by virtue of his ostensibly increased dangerousness. But, this effect has never been demonstrated experimentally.

Allen and colleagues (2019) sought to directly test this pattern. After presenting a large sample of 330 participants with a criminal case summary describing a sexual assault, participants were prompted to render an initial sentence recommendation. Next, participants were informed about the defendant’s mental health status using evidence of disorder described either as neurobiological or psychological, and treatable or untreatable. Participants then had an opportunity to amend their original criminal sentencing judgments and were able to allocate time between prison sentencing and involuntary hospitalization however they saw fit.


As hypothesized, neurobiological evidence elicited both shorter prison sentences and longer involuntary hospitalization terms compared to equivalent psychological evidence. These same effects were also observed when analyzing a participant’s change from baseline sentencing recommendation (see Figure 1). As hypothesized, decreased prison sentence length was accounted for by a change in deontological concerns — i.e., participants within the neurobiological condition found the defendant as less morally responsible and blameworthy for his actions, compared to those in the psychological condition.

Fig 1. Punishment change score by condition. Bars denote the percentage change in time from individual baseline punishment rating across conditions, for their revised prison recommendation (dark grey) and recommendation for involuntary hospitalization (light grey). Standard error bars shown. Image republished with permission from Corey Allen and PLOS ONE from

Overall, the experimental findings suggest that when mental health evidence is presented as having a neurobiological cause, laypeople are likely to assign more importance to it. Paradoxically, this effect seems to both favor and disfavor the defendant, depending on the punitive options available. That is, though prison sentences may be mitigated by the presentation of neurobiological evidence, the same evidence may increase the defendant’s risk of being involuntarily hospitalized.

These observed effects may have far-reaching implications for the law, which regularly confronts questions about the quality and presentation format of mental health evidence. For example, how can policymakers best manage the observed effects? Should neurobiological evidence always be accompanied by corresponding psychological/behavioral evidence or even warnings of potential biasing effects? Should jurors be made aware of treatment options or mandates in the case of excuse by mental illness of the defendant? Should judges receive a legal education on neurobiological evidence? Additional work is needed to answer these questions and explore other practical applications of this research.

These findings are described in the article entitled Reconciling the opposing effects of neurobiological evidence on criminal sentencing judgments, recently published in the journal PLOS ONE.

About The Author

Corey recently moved to Atlanta from Denver after graduating from Regis University with his BS in Neuroscience and BA in Philosophy. He worked as a lab tech at CU Anschutz, applying transcranial magnetic stimulation in clinical trials. He is currently a PhD student in Eyal Aharoni’s lab, researching the neuroprediction of recidivism, and the ethical issues surrounding such modes of risk assessment.

Corey’s concentration and interests lie in neuroethics and the moral/ethical implications that come with the advancement of knowledge and technology in neuroscience.

Dr. Aharoni's* current research investigates the application of neuroscience to the law and the impact of emotion and cognitive bias on criminal, moral, legal, and political decision making. Aharoni served as a Research Associate for the RAND Corporation. Aharoni completed a postdoctoral fellowship with appointments at The MIND Research Network for Neurodiagnostic Discovery and the University of New Mexico Psychology. Aharoni earned bachelor’s degrees in psychology and religious studies from the University of California, Santa Barbara (UCSB).

He earned a Ph.D. in psychology at UCSB where he also served as a research fellow for the MacArthur Foundation’s Law and Neuroscience Project.
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