Does nurture even matter? A look into the minds of killers

Jeffery Dahmer. John Wayne Gacy. David Berkowitz. Richard Ramirez.

These names send shivers up our spine and make our skin crawl. They are some of the most infamous serial killers of all time, and with the popularity of true crime rising, many of their stories have become hit shows on Netflix. But these men have something else in common – serious head injuries.

Many of us have heard about the potential link between brain injury and violent behaviors, but has this link been backed by science?

The relationship between criminal behavior and head injury has been a hot topic of debate in the scientific community for years, but a recent study from the Darby group at Vanderbilt has the potential to shift the common school of thought in a new direction. They discuss the possible link between brain lesion network localization and criminal behavior.

In other words, the Darby group is trying to determine if there is any connection between specific brain networks and criminal behavior. Brain networks are classified as widespread brain regions that show functional connectivity, meaning that different areas of the brain can be a part of one network controlling specific processes like moral decision making, fear, and even reward.

A brain lesion is an area of damaged brain tissue caused by injuries or medical conditions like cancer or congenital defects present from birth. Following certain brain lesions, previously normal patients can exhibit abnormal behavior.

"Lesions linked to criminality seem to cause issues in regions controlling value-based decision making and theory of mind, which are subsets of the larger moral decision-making network."

-- Rachel Biggs

A famous example of brain injury impacting behavior was a man named Phineas Gage. Gage was a railroad foreman considered to be great at his job and a nice, well-rounded person. But one day, Gage was using a tamping iron to tamp down some explosive powder that suddenly detonated. The tamping iron that he was using shot through his cheek into his brain and landed several feet away taking a large piece of Gage’s head with it. After this horrific accident, Gage’s friends noticed that he was no longer the friendly Phineas of the past, but a crude, aggressive monster that seemed incapable of controlling his own impulses.

This was one of the first cases that allowed scientists to link brain injury to a shift in personality. But sometimes brain lesions can cause more serious damage than altering a person’s personality.

Charles Whitman, now known as the “Texas Tower Sniper”, was a former marine that murdered 16 people at the University of Texas at Austin after murdering his wife and mother in their homes.

It was later discovered that Whitman had a brain tumor in his right temporal lobe, which is involved in learning and remembering non-verbal information. This area of the brain has also been shown to be implicated in episodes of increased aggression in patients with injuries or malformations there.

Whitman’s case has sparked much debate over why some brain lesions might lead to criminal behavior while others do not. Currently, there is no widely accepted explanation for this discrepancy.

To address this gap in knowledge, the Darby group was motivated by the phenomenon of diaschisis, or the observation that neurologic symptoms can be caused by dysfunction in a remote brain region that is part of the same functional network as a brain lesion, rather than only being directly caused by the brain lesion itself. This suggests that networks can be affected by lesions throughout the brain.

For this study, they used a technique called lesion mapping which can potentially account for these remote effects of lesions by comparing the connectivity patterns of those patients against a database of resting state connectivity from normal subjects. They used this technique to test whether lesions associated with criminal behavior are part of a common brain network, and if this network overlaps regions activated by neurophysiological processes that are often thought to be abnormal in criminals.

This study examined 17 patients with a documented relationship between a brain lesion and criminal behavior. Cases included documentation of no criminal behavior before the lesion or resolution of criminal behavior after treatment of the lesion. The 17 lesions were located throughout the brain. Lesion network maps from each patient were overlaid to determine brain regions significantly connected to all or most lesions causing criminal behavior. Statistical analysis showed a pattern of connectivity that specifically associated with lesions causing criminal behavior and not with lesions causing other neurologic symptoms.

These results suggest that lesions in different locations that are associated with criminality are characterized by a unique pattern of brain connectivity. Thus, while these lesions are spatially diverse, they seem to be part of one common functional network.

The next step in this study was to determine which functional network is linked to the development of criminal behavior. They hypothesized that lesions associated with criminal behavior would be functionally connected to regions involved in moral decision making in normal patients. By comparing data from their criminal group to data from normal patients when making moral decisions, they quantitatively concluded that lesion locations temporally associated with criminal behavior were functionally connected to regions activated by moral tasks. This connectivity was also significantly greater when compared to those with lesions that caused other neurologic symptoms. This shows that lesions implicated in criminal behavior, rather than other neurologic syndromes, appear to be linked to the brain network controlling moral decisions.

Moral decision making incorporates several different neuropsychological processes including cognitive control, value-based decision making, theory of mind (the ability to predict the actions of others based on perception of their mental state), and empathy. For the next step of this study, the researchers aimed to align lesion locations with these moral decision-making compartments. 

"Different locations that are associated with criminality are characterized by a unique pattern of brain connectivity. Thus, while these lesions are spatially diverse, they seem to be part of one common functional network."

-- Rachel Biggs

Using a program called Neurosynth to perform unbiased meta-analyses of the subcomponents, they found that lesions associated with criminal behavior were functionally connected to regions involved in value-based decision making and theory of mind, but not with empathy or cognitive control. Again, the connectivity observed in this analysis was specific to lesions associated with criminal behavior when compared with lesions causing other neurologic syndromes. These findings indicate that criminality may come from the inability to make value-based decisions or predict the behaviors of others, and not the inability to feel empathetic or issues with cognitive control as many have assumed.

To further support their findings, similar analyses were performed on a second group of patients that had an uncertain correlation between lesions and criminal behavior. From this second group they found no significant difference in connectivity when compared with their original cohort. Together, these data suggest that criminal behavior is likely a result of abnormal functioning in the neuronal network controlling moral decision making.        

The results of this study showed that seemingly disconnected brain regions can function as one connected brain network. Lesions linked to criminality seem to cause issues in regions controlling value-based decision making and theory of mind, which are subsets of the larger moral decision-making network.

These findings also suggest that empathy and cognitive control are not impacted in those exhibiting criminal behavior, which drastically shifts the current idea about which components of morality impact sociopathic behavior.

However, the exact psychological processes that are abnormal or disrupted in criminals remain unknown – just because someone has a lesion affecting this network, doesn’t guarantee that they will exhibit criminal behavior.

In fact, many criminals do not have brain lesions to explain their actions. For example, Ted Bundy, another infamous serial killer who confessed to killing over 30 young women, did not have any history of head trauma. After his execution, his brain was studied and scientists found no physical abnormalities that could explain his horrific behavior.

This study shows us that brain lesions temporally associated with criminal behavior are characterized by a unique pattern of brain connectivity, suggesting that it could be possible for a head injury to change someone for the worse. So rather than Netflix continually making new series on the lives of different serial killers, they could make one contrasting the tendencies of killers with head trauma or congenital defects with killers without any sort of head trauma or defects.