Article of Interest: Academic Chapter Examines the Use of Neuroscience Evidence in Brain Injury Cases Across 6 Countries

Professor Deborah Denno, Founding Director of the Neuroscience and Law centre at Fordham Law, has conducted an extensive analysis of how neuroscientific evidence regarding brain injuries influences criminal cases. Her research examines injuries caused by external factors, such as gunshot wounds or car accidents, as well as internal causes, including alcohol-induced brain damage or dementia.

The “Double-Edged Sword” Theory

A central focus of Professor Denno’s work is the “double-edged sword effect.” This hypothesis suggests that evidence of a brain injury could be viewed by the court as both a mitigating factor and an aggravating one.

However, after reviewing empirical research across six countries, Professor Denno argues that this framework is outdated. She suggests the concept is fueled by misunderstandings and does not fully reflect the reality of legal outcomes.

Did You Know? In the United States, the mention of brain injuries in criminal cases increased from 4–5% between 1900 and 1980 to 14% in the year 2020.

Findings from the United States

Professor Denno examined 7,776 defendants from 1900 to 2020, nearly half of whom faced the death penalty. Her study found that brain injury information was raised in 7.73% of these cases.

The data revealed that claims of “future dangerousness” related to neuroscience evidence occurred only 4% of the time. In cases where future dangerousness was raised, 65% of the risk was explicitly linked to the brain injury itself.

The research highlights a distinction in how courts handle mitigation. While U.S. Courts consistently view cognitive or intellectual deficiencies as key to mitigation, the prospect of rehabilitation is rarely a factor due to the presence of the death penalty or harsh sentencing.

Expert Insight: Samantha Carter notes that the tension in these cases often lies in whether a permanent brain injury is viewed as a reason for leniency or as a sign of an untreatable risk. The stakes are highest in capital cases, where the lack of focus on rehabilitation can fundamentally alter the impact of medical evidence.

Global Perspectives on Neurojustice

The study compared the U.S. To five other countries—Australia, Canada, England and Wales, The Netherlands, and Slovenia—none of which utilize the death penalty. Professor Denno identified a continuum regarding the double-edged sword effect.

A Place for Neuroscience in Criminal Law, Deborah W. Denno

Slovenia: An outlier with no double-edged sword effect, emphasizing rehabilitation and alternative treatment.
Australia: Some evidence of the effect, though a 2023 study found neuroscientific evidence led to leniency in 85% of sentencing cases.
The Netherlands: The effect appears in cases with high risks of severe violence, yet mitigation remains possible through opportunities for improvement.
Canada: A double-edged sword effect exists, potentially due to a lack of treatment alternatives and the presumed permanency of injuries.
England and Wales: On the furthest extreme, where the prosecution is more likely than the defense to introduce neuroscientific evidence.

Legal Implications and Future Outlook

The significance of these findings is illustrated by cases like United States v. Runyon. In this instance, the U.S. Court of Appeal for the Fourth Circuit agreed that defense counsel should have introduced brain injury evidence as a mitigator, reversing a lower court’s dismissal.

Based on this research, defense attorneys may become more confident in presenting neuroscientific evidence. The data suggests the risk of the “double-edged sword” is likely too low to justify withholding evidence of a brain injury.

Future legal strategies could shift toward a more consistent application of neuroimaging tests, such as MRIs, and psychometric tests to secure mitigation, even when injuries appear untreatable.

Frequently Asked Questions

What types of brain injuries were examined in the research?
The research explored both external causes, such as car accidents and gunshot wounds, and internal causes, such as dementia and alcohol-induced brain damage.

How does the death penalty affect the use of neuroscience evidence?
In the U.S., the prospect of the death penalty or harsh sentences means that the potential for rehabilitation is far less likely to be considered a relevant factor compared to countries without the death penalty.

What is the “double-edged sword effect”?
It is the hypothesis that neuroscientific evidence of a brain injury may be viewed by the court as both mitigating (reducing culpability) and aggravating (increasing perceived danger).

How should the legal system balance medical evidence of brain injury with the goal of public safety?