Deborah W. Denno

Neuroscience has become an increasingly common feature of criminal litigation, shaping everything from death penalty mitigation to juvenile sentencing. Yet many of the assumptions surrounding brain science in the courtroom remain wrong, Fordham Law School Professor Deborah Denno told Law360.

As the founder of the Fordham Law School's Neuroscience and Law Center, which marks its 10th anniversary this year, Denno has spent the past decade building one of the nation's most comprehensive databases tracking the use of neuroscientific evidence in criminal cases dating back more than a century.

Neuroscientific evidence is a broad term referring to data derived from the study of the nervous system and brain through a wide array of methods. It includes imaging like x-rays, CT scans and MRIs, but also psychological testing, genetic and family history information, clinical diagnosis and expert testimony.

The research shows that this evidence is used primarily to mitigate punishment. Prosecutors, meanwhile, have increasingly responded by arguing defendants are exaggerating or fabricating neurological and psychiatric conditions, Denno said.

As artificial intelligence promises to transform both neuroscience research and the justice system, Denno sees both opportunities and risks for courts.

In this Q&A with Law360, she discusses what the center's research has uncovered, why neuroscience has become indispensable in capital litigation and how AI could reshape the way courts evaluate criminal defendants. This interview has been edited for length and clarity.

What motivated you to found the center?

People's misconceptions were a major motivation for me. I had been attending conferences for many years. I teach criminal law and criminal procedures, so much of the focus in criminal law is on the brain and the mind and what people are thinking. I thought at those conferences that there was a vast misunderstanding among the participants about how neuroscience operated in the criminal justice system. At the same time, I didn't have enough data myself to have objective evidence to rebut some of the presumptions and myths. So, that was a major motivating factor.

Could you give me examples of some of those presumptions you were encountering back then?

Ten years ago and up to the present time, people mostly focused on about five widely publicized criminal cases, some of them going back over a century. One of those cases is decades old. It's called the Texas Tower case, where somebody climbed the tower at the University of Texas and ended up killing people with a rifle. Before that man even had a chance to leave the tower, he was killed, and a later autopsy found a tumor in his brain.

Another case from the 1800s involved Phineas Gage, a man who had a rod going through his head, and for the next 12 years he lived with the consequences of the physical damage caused by this rod. There's been an enormous number of myths about that case.

So, when people talk about the criminal justice system, these cases have been paramount. But these weren't criminal defendants at all, and even the assumptions about these people were incorrect. Number one, there was a focus on a very few highly publicized cases, about which a lot of times people got the facts wrong. Number two, there was a presumption that this [neuroscientific] evidence wasn't even in the criminal justice system, but I knew it was, because it's used widely in death penalty cases. And number three, the presumption that the use of this evidence could be extremely harmful to defendants. We've certainly seen aspects of that, but not nearly as much as people were playing it out to be. Mostly, this evidence is mitigating, and it could be very helpful to defendants.

Looking back over the last decade, what has actually changed inside courtrooms, and what turned out to be hype?

The hype is that this evidence is used in a very negative way, or that it's used to turn around a jury, in other words, to support what journalists often call "my brain made me do it" defense, that it totally gets the defendant off. There is no such defense anywhere, not in this country, and I don't think there's anywhere else in the world.

I have a criminal database where I look at every criminal case that's used neuroscientific evidence in any capacity from 1900 to 2020 and we're now collecting cases up to 2025. What I saw is that this evidence is mostly used as mitigation. But these explosive outcomes are extremely rare, and only show up in these highly publicized, very hyped cases.

How has the use of neuroscience evolved over time?

We've found a continuing fascination from the early 1900s and probably even earlier. For centuries, in England and other countries, the belief was that it was really the devil that was taking control of you. It was a very religious kind of explanation for why people acted in bizarre and sometimes very violent ways. But as time went on, we learned more about the brain. You had the Renaissance coming in and introducing science. There has been an increasing effort to try to understand how the brain is operating.

One way that we see that happening in the United States is literally by looking inside the brain. X-rays were created in Germany in 1895, so by 1925 you start seeing them used in criminal cases to literally look inside somebody's brain to try to figure out whether that brain looks abnormal. At that time, nobody really knew what was going on, but they could see that this defendant's brain looked abnormal. That evidence was introduced into court. Judges accepted that evidence.

In the 1940s, electroencephalograms started to come in. MRIs and CT scans began being used in the courtroom as well. You don't always have to do that with brain imaging. There are also non-imaging tests: standard psychological tests, expert testimony, for instance.

What findings from the center's research surprised you the most?

The most surprising finding to me was seeing a decline in use of the insanity defense. It's the oldest defense in the United States. We borrowed it from England that created this particular kind of defense in the mid 1800s. I actually thought that the insanity defense would be more widely used to see as a result of the introduction of neuroscientific evidence. It's actually plummeted in use. So, you see it widely used in the early 1900s, but now it's just about 10% of the cases.

The second thing that really surprised me is that there's an increase in claims that people are lying about their symptoms, lying about mental illness. In criminal law, this is called malingering. It's a very effective strategy for prosecutors to use to try to get this evidence out of court.

You mentioned malingering. How are courts responding when prosecutors argue that defendants are exaggerating or faking neurological or psychiatric conditions?

This is a persuasive argument to make to courts, particularly if they have a bias against claims of insanity to begin with. Prosecutors are lining up experts to question this evidence, and what we're finding is that defense attorneys aren't really very prepared to counter it.

Defense attorneys spend all their time trying to argue for an insanity defense, but when a prosecutor starts making claims that their client is malingering, the defense isn't very well prepared to counter them. A lot of times they don't bring in an expert at all, which is really not a good thing. Attorneys should really learn how to counter these arguments, and to find experts right away.

How has neuroscience changed capital litigation over the last decade?

These changes have been huge. Neuroscientific evidence is particularly pronounced in the penalty phase of a death penalty case, which has grown hugely over the last decade. We now have mitigation experts, people who are highly trained in finding and investigating mitigating evidence.

We have measured the length of mitigation cases: the earlier ones in the early 1900s are about 30 pages. In the 2020s, many cases are up to 200-250 pages. Much of that is the "battle of the experts" but also the "battle of the evidence" that plays out in court. These mitigation experts do an enormous investigation of the defendant. We're not going to find these in all cases, unfortunately. But if it's a sophisticated attorney, we'll get a vast amount of information about the defendant and their early history.

In major cases, such as the Boston Marathon bombing case, attorneys will also do a genetic history and go back, say, four generations on a defendant to see if there's genetic evidence of insanity, depression or mental illness, in addition to all kinds of evidence on school history, work history, family history. It's been an enormous change.

From covering habeas proceedings, I've noticed that many death row inmates sentenced decades ago received little mitigation investigation during their original trials. Does your research reflect that?

Yes, definitely. I mean, we see a wide range of quality of defense attorneys, which is really troublesome. At the guilt stage, that's where you should have much of the mitigating evidence, so that the defendant doesn't even get into the pipeline to the death penalty. Many times, attorneys do very little at that point, and it's only later when you get the big New York law firm coming in, and spending thousands of dollars on a case, that you see mitigating evidence. Sometimes it's a bit too late.

Given advances in neuroscience, do you think habeas law should evolve to better accommodate new scientific evidence?

Absolutely, because the science has grown, but habeas law has not. It is extremely restrictive, and our vision of the human brain and human behavior has become much more knowledgeable over time. So I do see a call for less restrictions, or for changing perceptions or wording of the insanity defense. That in many states in this country — at least half the states — we're still using a definition of it that evolved in the middle 1800s in a different country is really troublesome.

How influential has neuroscience become in the context of juvenile culpability and sentencing?

Neuroscience has been hugely influential, starting with the earlier cases on juveniles — Roper v. Simmons, etcetera. It's been a driving force in those cases, and the Supreme Court has been open to it. Neuroscience is probably the reason why juveniles who were under age 18 at the age of their crimes are no longer executed. It's been a continuing barrier to prosecuting individuals with a low IQ or with some intellectual impairment.

How closely connected are neuroscience and artificial intelligence from a legal perspective?

Neuroscience is the foundation of AI. The aim of artificial intelligence, from the very beginning and up to the present time, has always been to mimic aspects of the human brain. So, the more we know about how the human brain operates, the more we can develop AI strategies — hopefully for the better, but as we've all seen, it's also for the worse.

How this is going to play out in the courtroom gets a little bit trickier. What's going to happen is, with AI we're going to have a better ability to see how the brain works, and that could be for the better. There's still a little bit of skepticism, but it decreases with every passing talk I give. I think judges are much more open to neuroscience than they were in the past.

In addition, we see AI being very effective in areas such as Alzheimer's or dementia, or making new discoveries. I see those kinds of discoveries potentially being very helpful in the courtroom for defendants. One thing we're lacking is the ability to compare a certain defendant to other people. In a malingering case, very often a prosecutor can say, "well, their brain doesn't really differ all that much from somebody else's." I think AI may be able to change that. It may provide us with more systematic information on that front.

Are you concerned about courts eventually relying on AI to assess or predict defendants' behavior?

Absolutely. There is a value, in theory, in having judges and courts and human beings evaluating a criminal defendant, seeing that defendant as a human being rather than just as a statistic. There is a concern that the justice system has gotten very quantitative or statistical, when in fact the whole reason we have courts and juries is to look at the human element. This is what mitigation experts are all about. If it gets very statistical, that component could be entirely lost, and I and others are very concerned about that.

Is there anything you think lawyers and judges still get wrong about the brain?

I see an enormous amount of bias when it comes to trying to connect a brain abnormality with human behavior, because we haven't yet gotten to cause and effect. A good attorney is not going to say that an abnormal brain caused a certain kind of behavior.

What we're really talking about is: did this condition heighten the likelihood that someone would have acted rashly and engaged in a kind of behavior that we find illegal? It's all sort of a probabilistic determination, and the courtroom is full of probabilities. "Beyond a reasonable doubt" and "clear and convincing evidence" are based on a probabilistic determination.

And if you're looking at neuroscientific evidence, you should be looking at it in the same way.

If you consider this evidence, does it heighten the likelihood to a considerable degree that this person engaged in behavior that they wouldn't have engaged in otherwise? I would wish judges would consider that kind of approach much more, and maybe they would look at an outcome very differently as a result of that.

You told me that neuroscience plays a bigger role in the justice systems of other countries than it does in the United States. Why is that the case? Does it have to do with the fact that the American justice system tends to be more focused on retribution and punishment than to rehabilitation?

Absolutely. That sort of punitive focus is something to battle when you're trying to introduce neuroscientific evidence or get a fuller picture of the human brain. You would think judges, before imposing what we typically see as a very harsh punishment, would want a full view of the person before them.

–Editing by Alex Hubbard.

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