Quirks and Quarks

Could brain scans determine guilt?

Neurolaw is on the rise and it could change the landscape of crime and punishment.
Brain scans can show the difference between acting with knowledge or recklessness when it comes to criminal intent. (Scott Olson/Getty Images)

Neurolaw is a growing field of study in which brain scans are used to help determine degrees of guilt or criminal intent.  A recent study by Dr. Read Montague, a computational neuroscientist at The Virginia Tech Carilion Research Institute, may help judges and juries determine a person's intent while in the act of committing a crime. 

For lawyers like Jennifer Chandler from The University of Ottawa, neuroscience will have a greater influence both in the courtroom and at the legislative level in the future. 

The following interview has been condensed and edited for clarity. 

Bob McDonald: What was your interest in studying the relationship between the brain and criminal activity? 

Reid Montague: It comes from a long term investment into the area of neuroscience and law over the last decade. And the question at hand is a bit of a controversy in the legal space. These mental state distinctions are: doing something purposefully, knowingly, recklessly, or negligently. Those are the four different categories. If you and I committed the same criminal act with the same circumstances and elements of the crime, and you did it in one particular mental state and I did another, you might get probation. I might go to jail for 25 years.

So other than something about your brain that kills you, I can think of nothing more important than depriving you of your freedom predicated on mental states, and people have claimed that these aren't really real.

These are just mechanisms used by the enfranchised to keep them enfranchised, and to keep disenfranchised people, disenfranchised. In other words they're just tools of the social and political trade.

BM: Why did you focus on knowledge versus recklessness? 

RM: The reason we went after "knowing" and "reckless" is when you give people various vignettes designed by lawyers, and teach them what "knowing" and "reckless" is and let them judge what side of the boundary they were on, given these various vignettes, they're very bad at that category. They're very bad at that boundary, that boundary is poorly defined with respect to prospective jurors. And so we wanted to go after that kind of "greyness" there.

BM: So it's a fuzzy boundary.

RM: It is a fuzzy boundary and behavioral practice. That's right.

BM: Take me through your experiment. How did you find out the difference in brain stage between someone acting knowingly and someone being reckless.

RM: We parameterised the knowing part and we parameterised the reckless part. Let me explain to you what I mean by that.

So we offer people the possibility of carrying an attache case across a barricade, a boundary. Let's consider the boundary a TSA site in an airport or the boundary going from Mexico to the United States. They're told there's contraband in it. So what we avoid in our experiment is the idea that you're carrying something illegal, but maybe it's just inappropriate.

So you're offered to carry the cases over and over again, you do repeated play here. You do one run and you do another and you do another, and we ask you whether or not you're going to carry the case. You may be shown one case that you ran, and that one case does contain the "stuff" or you may be shown up to five cases, which means there's a one in five chance that you're carrying.

So that parameterizes "knowingness" with "full knowingness" with one case and one out of five chance at five cases.  And we do all the numbers in between for everybody. So that's the knowing part.

The reckless part is, as you come up to the barricade, the boundary, there's a possibility of being detected by guards at the barricade. And that's also parameterized between zero percent chance of being caught, all the way up to 80 percent chance of being caught. The first part is the knowing part and the second part is the the reckless part. And we study this across people doing it and all sorts of combinations.

So we were looking for what things change in your brain as we go from perfect knowingness to more and more recklessness. So instead of just searching for a hard boundary we parameterised the transition from perfect knowingness to more reckless.

BM: OK. Now let's take this to a legal case. Sort of more serious what would be the equivalent of this, a real life equivalent, of knowing versus reckless.

RM: So I get on a highway and the highway says 60 miles an hour is the speed limit. I don't see anybody. I go 80 miles an hour. So I know what the speed limit is. I go over the speed limit by 20 miles an hour. I accidentally run into a family of four and everyone's killed. OK. I was reckless. I was more reckless at 80 miles an hour than I would have been if I'd been driving 62 miles an hour.

Let's suppose that's what you did. Suppose I get on the same highway. The person driving the car with a family of four in it is somebody that's having an affair with my wife. I see them, I crash into the car, I kill everybody in the car. We make the inference that some part of me purposefully or at least knowingly crashed as well.

BM: OK. So getting back to your suitcase experiment. How did you examine the brains of your subjects.

RM: We did functional MRI imaging which looks at microscopic blood flow changes and uses that as a proxy for changes in neural activity. Subjects lay in the scanners during the presentation of the scenarios that we've  been talking through, and made choices about whether to carry the case each time.

We found that we could develop a mathematical mapping between the brain response to the choice at hand, and the state that they were in given the information that we provided. So the degree of knowingness could be mapped onto one network response, and the degree of recklessness could be mapped onto another response.

BM: What differences did you observe in the brains between those who were reckless and those who were knowing the differences were responses. 

RM: It's very hard to describe in words. One way I can characterize it is to say that we can very accurately decide whether or not you were in a reckless state a more reckless state or a knowing state. We were in the high 80 percentiles low 90 percentiles.

Research paper in The Journal Of Law and The Biosciences "The use of neuroscientific evidence in Canadian criminal proceedings"