By Tamara Sepper

Advancements in the study of the human brain promise to transform our criminal justice system. In recent years, courts have seen a significant upsurge in neuroscientific evidence, which includes brain scans like fMRI, PET, and EEG. Research that explores how much, if any, control we have over our actions — that age-old debate about free-will versus determinism — cuts at the roots of criminal law’s foundational principles: the presumption that conscious decision-making is behind most behavior and therefore retribution and deterrence justify punishment. In this inaugural edition of Office Hours, we explore neurolaw, the interdisciplinary field that explores how neuroscience discoveries impact legal rules and rationales. To help us understand how neuroscientific evidence is used in courts today and what’s around the corner, I spoke with Professor Deborah Denno, founding director of the Neuroscience & Law Center at Fordham Law School.

The following conversation has been edited for brevity and clarity

When do neuroscience and law most often cross paths?

You’ll see this interlinkage in a number of different fields. You’ll see it in tort law. You’ll see it in contracts, for example, whether somebody who’s signing the contract can fully understand what they’re signing. You certainly see it increasingly in elder law. Also, FDA law, such as neurotechnology and artificial intelligence; it really has a huge span. But the most significant use is in the criminal law, and it reverberates out to different kinds of fields. The reason for that is so many individuals who are convicted of crimes have brain injuries or some kind of brain problem that invites this kind of neuroscience to analyze what’s happening with their behavior.  

Is there a conflict between neuroscience and the foundational principles of criminal law?

Whether or not there’s a conflict between neuroscience and the foundations of criminal law is up to the observer. I don’t think there’s a conflict. I think neuroscience is very important for criminal law. Criminal law is all about mental states, and neuroscience is all about mental states. So, to me, it seems very consistent. I think if people do think there is a conflict, it’s based on misinformation.

You have written, “The entire modern criminal justice system is based on an outmoded psychology of mental states.” 

Absolutely. Much of criminal law is based on Freudian psychoanalysis. A lot of people don’t know that, but when the modern criminal law code was being developed in the 1950s and 1960s, many of the commentators and advisors on that code had a psychoanalytic background. In addition, Freud had a huge impact on the United States. It’s no accident that impact also infiltrated into the legal system. Many of our expert testimony evidence in criminal cases is based on this Freudian psychoanalytic foundation, which we really don’t identify with anymore in a modern world.

How much of what we have discovered about human behavior and how the brain works is accounted for by criminal law now?

I would say maybe it’s about a fifth there, and it’s increasing with every passing year.

Why do most criminal statutes require proof that the defendant committed an offense with a certain mens rea, or mental state, like knowingly, purposely, negligently, recklessly and so on?

Mens rea has always been critical since the 13th century, a critical component of whether or not we find somebody blameworthy or whether or not we want to punish them. The reason being is every crime has to have some level of culpability and blameworthiness. The feeling in the criminal law is if you punish somebody and they’re not blameworthy or culpable for what they did, that it’s a violation of our civilization, of our civil rights, and who we are as human beings, and we simply don’t recognize this as a proper way of treating individuals.

If it’s discovered that determinism is the correct way of understanding the brain, and that the “I” within us isn’t directing our actions, would it upend our criminal justice system? 

There may come a day where we find out that all of our behavior is determined, that determinism is what’s driving us and not free will at all. That wouldn’t surprise me. I think the more we find out about how people think and act, the more we may question how much free will we really have. If that’s the case, or if science starts encouraging us to look in that direction, then I think it would be imperative for us to completely rethink our criminal justice system.

Right now, our criminal justice system is based on the feeling that there is free will, that we all have control over our behavior. Indeed, even in the 1960s, when we were revising our criminal justice system, the individuals writing the code recognized that we have to act as though people have free will, even if they don’t. That’s just the only choice we have at this point. But that new science may change that. I think we’re going to have to change entirely how we approach any kind of incarceration for individuals who may be uncontrollably violent, et cetera. I think we’re going to have to change our society entirely. My hope is that we can start thinking about those changes now, even if we end up finding that we do have free will.

Is there a difference between the brain and the mind?

There’s been a longstanding debate on whether there’s a difference between the brain and the mind. I think that somebody’s answer to that would depend on how much they embrace determinism and the feeling that we have any kind of control over our behavior. If you’re a determinist, you’re going to think they are probably pretty closely one and the same. If you’re someone who has even a feeling that we might have a sliver of free will, you may think that there’s a difference between the two.

I romanticize these kinds of arguments. I like to think that, even though so much of our behavior is determined unconsciously, I’m still holding out hope that there’s a sliver of free will there, in which case, the answer would be we have a brain. We have a mind. Maybe the mind isn’t as large as we thought it was, but we still have a little bit of it.

How do you see the legal system responding to technology that can read our thoughts?

I think when we have a world where we are all relying on new technology that can read people’s minds or figure out people’s thoughts, we’re going to be in a very different kind of society than we are now. This kind of technology changes every aspect of our lives. So our legal system will change accordingly. It’s not as though our legal system is going to be in one world, and we’re going to be in a different kind of world that doesn’t recognize this technology. It’s going to affect our view of criminals and how we think of punishing them.

This is all going back to the way much of our criminal justice system was historically. Sigmund Freud and Freudian psychoanalysis started having a large impact in our country in the early 1900s. That impact didn’t change just our criminal justice system. It changed our entire society and how we all viewed the world and how we all viewed mental states. So I imagine that any kind of new technology and neurotechnology will do the same thing. 

What’s the practical value of philosophical debates that neuroscience often sparks, especially as its findings relate to law?

Philosophy has always served as the foundation of the criminal law, and it gives the criminal law guidance, particularly since criminal law is based so much on our morals and our normative system. At the same time, I don’t think philosophy should outweigh or dominate our approaches to looking at neuroscience in the context of the criminal justice system. I think it’s much more important as well to look at research and to see how neuroscience is being used in a practical way.

One reason I started doing the research I’m conducting right now and continuing to do is because I felt there wasn’t enough practical information on the use of neuroscientific evidence in the criminal justice system. I thought some of the claims and conclusions that were being made were faulty, and I’ve since discovered they really are. Once you start looking at neuroscience in the criminal justice system, we realize that there were a lot of myths and misconceptions about its use and applicability. So I would like to think that we still need this philosophical and moral foundation, but, at the same time, we need much more research to investigate how neuroscientific evidence is being used in the criminal justice system and how it can improve where we’re going, particularly in the area of incapacitation, how prisons are operating, and how we punish individuals.

When do courts most commonly admit neuroscientific evidence?

Neuroscience evidence is submitted in criminal cases in about three major ways. Number one is it can be admitted at the guilt phase to determine whether or not a defendant is guilty or innocent, in other words, whether they are privy to the insanity defense or diminished capacity, whether we’re going to convict them of a crime.

The second major way is at the sentencing phase. This occurs a lot in death penalty cases. When you’re trying to evaluate whether or not, say, a jury is going to sentence a defendant to death or not, neuroscience evidence comes in, in a major way, to explain why the defendant did what they did and why we may want to sympathize with them or better understand the reasons for their extreme violence, or something to that effect. 

A third way it enters the criminal justice system, which I’ve found in my research, is it’s used by prosecutors to measure the degree of injury that a victim might have experienced. These kinds of cases predominantly are shaken baby cases. 

You have written that in shaken baby syndrome cases, prosecutors are “permitted to concoct intent out of brain scans that were submitted for the sole purpose of presenting the victim’s injury.” Why do judges allow prosecutors to expand the scope for which the evidence is admitted?

Shaken baby syndrome is extremely controversial because prosecutors do rely on brain-scanned evidence to assess the nature and degree of whether shaken baby syndrome occurred at all, and the extent of the injury. Prosecutors will use that injury to argue that a defendant intended to shake or injure a child. In many of these cases, a child is actually killed or murdered. So the prosecutor will look at the injury and explain the defendant’s mental state based on that injury. 

That’s several steps away from how we usually look at intent in criminal law. Usually, you look at the defendant’s mental state and whether they were suffering from some kind of trauma or brain injury. But to look at the victim’s injury and assume from that a defendant’s level of intent is several steps away. Judges accept this evidence because sometimes they simply don’t understand it. That’s number one. And, sometimes, experts testifying in court will steer judges in that direction when they really shouldn’t.

You’ve found that, despite the belief to the contrary, prosecutors don’t use neuroscientific evidence to argue a defendant is predisposed to violence and presents a danger to society…

While prosecutors do make that argument sometimes, they don’t make it nearly enough or as much as people had anticipated. There’s several reasons for that. Number one is prosecutors are concerned that this is going to cause juries to be much more sympathetic to the defendant than aggravating or angry at the defendant. It’s a toss of a coin. But, almost always, prosecutors want to get it out of the courtroom. Defense attorneys want to get it in. That’s a statement in and of itself.

The biggest way that prosecutors use it is they will make the claim that defendants are malingering. In other words, the defendants are lying about this brain injury and this brain trauma that they have. And there are tests of malingering that can be conducted on defendants that might show that the defendant is lying. I’ve seen a huge increase in prosecutors using these malingering tests if, in fact, defense attorneys introduce it in court.

How do these malingering tests work? 

I mean, first of all, malingering tests range in quality and variety. But, basically, a common test is for a psychologist to question a defendant about a claim that they’re making about some kind of trauma that they have or some hallucinations that they may be having. It’s a series of questions that may test whether or not a defendant is lying. 

Now, there’s a lot of controversy on how good these tests are and how valid and reliable they are. Nonetheless, it’s pretty powerful evidence to introduce that into court, particularly if a neuroscientist or some kind of psychologist is able to make the claim that the defendant is lying. That said, a strength of neuroscientific evidence is to show that somebody can’t fake an MRI or frontal lobe damage or a brain tumor or something like that rate. Usually, these malingering tests come in when the injuries are more subtle, and the measurements of them are more subtle.

Scientists have discovered that our brain function and structure is constantly shaped by the environment and our experiences; what’s called neuroplasticity. What are the takeaways of this discovery for how we incarcerate individuals?

One of the most important contributions that neuroscience has made to the criminal justice system and to the legal system generally is to show us how incredibly ineffective and dangerous and self-defeating prisons are. We already know that prisons are an environment that make it much worse for individuals who have some kind of brain damage or brain trauma or challenges. We have to change the environment, acknowledging that most people in prisons have some kind of mental illness or brain trauma. Once we recognize that, we can start to create an environment that’s less punitive and less retributive, and much more going with the goal of rehabilitation or helping people with mental illness and brain trauma, helping them to get jobs, for example.

Here’s a hypothetical: brain scan evidence shows the defendant has a large tumor in his brain that cannot be safely removed. An expert testifies that without doubt the tumor caused him to lose control over his impulses when he shot and killed his boss who was taunting him and that such violent outbursts are likely to repeat in the future. So we know that the killing was not a deliberative choice and that he could present danger to society. What is the right response in this scenario?

Every case involving neuroscientific evidence or any kind of evidence always brings up moral and normative questions that we have to decide as philosophers or members of a community. Neuroscience can only help us so much in making that kind of determination. If there is a situation where a defendant has a brain tumor and it can’t be removed, and an expert testifies that there’s some likelihood that this tumor might be affecting the defendant’s behavior, then it becomes more of a moral and normative decision that we make. There comes a point where the science ends, and we, as a community or as a civilization, have to decide what we want to do with someone.

We could say this person might be a danger in the future. It’s maybe unclear whether they’ll ever be a danger, but at least there’s some likelihood they may be dangerous, and we may want to incarcerate that person because of that likelihood of danger. Number two, we may develop or come up with a situation where we put that person on probation, where they have to check in and report to someone regularly, and say how they’re feeling medically, or whether they’re having violent impulses, or something like this. I mean, this is the case with some sex offenders, for example, who may have urges their entire life.

Number three, there may be a decision, and there has been in some cases. It could be very controversial, where there could be some kind of medical intervention. Say you can’t remove the tumor without purportedly killing this person, but there may be other ways of attempting to control their violent impulses by inserting a brain implant or something like that. We as a society have to decide what kinds of decisions we’re going to make in these kinds of cases.

We haven’t gotten there yet, but we certainly will because there’s growing evidence that it’s just around the corner, that we’re going to be able to read people’s thoughts. There’s certainly enough going on there that, number two, we’re already having scientists insert brain implants for some individuals who have epileptic seizures, et cetera. So, if we can have some kind of medical intervention for a defendant that could control their potentially illegal behavior, I suppose, at some point, we’re going to have to decide whether this is normatively or morally acceptable.

What’s the difference between neuroscientific evidence and behavioral genetics evidence?

Neuroscientific evidence and behavioral genetics evidence often overlap. In my research, I separate the two because legally, courts treat those arguments very differently. With behavioral genetics evidence, it’s a much narrower kind of argument. Typically, in these cases, a defendant’s going to claim that, based on some kind of genetic condition, in other words, something that they have inherited or received behaviorally across generations or directly from their parents, that they act the way they do. This has come up in a number of cases. A classic case is this Susan Smith case that happened some time ago. This was a woman who drowned her sons. She put them in a car, she herself jumped out of the car, and put the car in the lake, and they drowned. She blamed somebody else for doing this. Her attorney, David Bruck, made a number of arguments on her behalf. One of the major arguments that didn’t get as much press was that she had a family history of very serious depression. Her father had depression, her grandparents had depression, et cetera. In many of these really highly publicized death penalty cases, attorneys will go back to sometimes the 1800s, in terms of a family tree, to see the lineage of any kind of passage of some kind of attribute that may be genetic. That could include depression, mental illness, alcoholism, you name it, that might have heightened the probability that someone would engage in a very violent behavior relative to other kinds of people. This is going to be different from neuroscientific evidence, which is much more present oriented and based on that particular defendant and their brain makeup. 

If you could answer any question at all within your lifetime, what would it be?

Well, there have been a lot of books saying this, but one of the last remaining mysteries, something that we haven’t figured out, is how to measure consciousness and human consciousness. Scientists have long tried to measure it, and scientists from every conceivable field, and they still don’t get it. What makes us consciously aware of what we’re doing? And so I’d love it if we could measure that. Someday we will. But we haven’t done it yet.

To get future editions of Office Hours in your inbox, subscribe for free at