Conversations with Ryan Darby: Between brain lesions and criminal behavior

Ryan Darby is an assistant professor of neurology at Vanderbilt University. He investigates neuropsychiatric disorders where what makes us human, such as our identity as a self or our capacity to behave morally, is impaired.

He is currently working with moral psychologists at Harvard to develop novel psychological tests of social and moral behavior in patients with frontotemporal dementia which correspond to behaviors in real-life, predicting that these will align into two moral aversion networks in the brain: a harm-aversion network and an disgust aversion network. Impairments in each of these should correspond to specific abnormal behaviors in these patients.

SCIENTIFIC INQUIRER: First off, what prompted you to investigate the links between brain lesions and criminal behavior?

RYAN DARBY: I run a frontotemporal dementia clinic, where previously normal patients often present after committing a crime for the first time as an adult. I wanted to understand whether there are certain areas of the brain that, when damaged, would lead to criminality. The easiest way to answer this question is to look at patients with focal brain lesions, where you can clearly identify the area of the brain that is damaged.

SCINQ: How exactly do lesions change a person’s personality so much that they can swing from law-abiding to criminal or non-violent to violent? Is the mechanism well understood?

RD: We don’t entirely understand how brain lesion’s change a person to make them more or less likely to commit a crime. One question is where brain lesions in the brain that contribute to criminal behavior occur, which we tried to address in our study. A second question is what psychological processes become impaired that are associated with criminal behavior. We could not directly test this because we did not test the patients. However, we looked at what functions the areas of the brain normally are involved in where these lesions occur, and found they were normally involved in moral decision-making.

SCINQ: How did you design your study and what did you discover?

RD: We identified cases from the literature where a patient was described as being previously normal, suffering a focal brain lesion, and then developed criminal behavior. We found that these lesions occurred in several different locations in the frontal and temporal lobes. We next used a new technique called lesion network mapping to test whether these lesions in different locations were functionally connected to the same brain network. We found that all of the lesions were connected to the same brain network, and that the brain network is one that is typically involved in moral decision-making.

SCINQ: Can you discuss the notion of the connectome and how you employed it in your study?

RD: The connectome is a wiring diagram of the brain. If you think of a map, there are cities, and then there are all the roads connecting those cities (the connectome). We use the connectome to see if brain lesions can occur in different locations, but they are all connected to the same network (like if many different cities had roads connecting to one common city). Brain areas don’t work in isolation, so the connectome tells us the network of different brain regions that work together. These networks are probably important for the most complex human behaviors.

SCINQ: You found that lesions along a network dealing with moral decision making were associated with criminal behavior but are there possibly other factors at work as well?

RD: We found that the lesions occurred in a network of brain regions implicated in moral decision-making. However, moral decision-making is complex and involves many different psychological processes. We found that the network we identified aligned most closely with “value-based decision-making”, which is what helps to give decision a positive value (making them rewarding) or a negative value (making one avoid those decisions).

SCINQ: Were particular types of behavior more common than others? Does the size, location, or quantity of lesions matter?

RD: Because we searched for published cases, these tended to be more “extreme” examples, such as murder, rape, or assault. However, similar lesions caused non-violent crimes. We had a very small sample size, so we weren’t able to tell if there were subtle differences between types of crimes, but in general all types of crimes have this same pattern.

SCINQ: If lesions can cause criminal behavior, in theory, can they also do the opposite to someone who exhibits criminal behavior?

RD: That is a very interesting question. One idea is that moral decision-making involves a balance between competing brain networks. If that is the case, then it is theoretically possible that lesions to the competing network would change people’s behavior and make them less likely to commit a crime. However, one must be very careful with this idea; there is a long history of trying to treat criminal behavior with frontal lobotomies, which can take away a patients motivation to make any decision. I am not aware of any report of a naturally occurring brain lesion resolving one’s criminal behavior.

SCINQ: What’s next in terms of research for you?

RD: I treat and study patients with frontotemporal dementia, who also commonly commit crimes as a result of their brain disease. We are planning to test if they also have abnormalities in this same brain network, and differences on moral decision-making tasks.

SCINQ: How did you come to a life in science? Did you always want to be a scientist

RD: I’ve always been very curious about the world, but didn’t always know I wanted to be a scientist. I also liked a lot of my philosophy and humanities classes as well. But when I took a course in cognitive neuroscience, and discussed patients with neurological injuries, I knew that this was what I wanted to do with my life. It combines fundamental questions about humanity (morality, belief, our perception of free will), and studies this using scientific approaches. I also love being able to work with patients, which is difficult but also very rewarding.

SCINQ: Finally, what fascinates you the most about the human brain?

RD: So many things! I am most fascinated by understanding the most complex and interesting facets of what make us human, and one way to do this is by studying patients where neurological injuries have disrupted these processes. So, we study patients with abnormal beliefs (leading to delusions), abnormal perceptions of reality (leading to hallucinations), abnormal morality (leading to criminal behavior), and abnormal free will perception as a result of neurological injuries.

IMAGE SOURCE: Dmitry Tolkachev

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