Disclaimer: This text should obviously be read as scientific popularization rather than rigorous scientific work. All references this text was based on are cited at the end.
It is a well-known fact amongst true crime enthusiasts that head injuries are disproportionately common in serial killers. Whether we’re talking Jerry Brudos, Richard Ramirez (who suffered two) or David “Son of Sam” Berkowitz (who suffered three!), it seems like most serial killers were hit on the head at some point in their life. Truth is, brain injuries are common in criminals, more than they are in the general population. But why is that? And do all brain injuries lead to criminal behaviour? Will your cousin Timmy, who dove into an empty swimming pool, kill his dog? As both a true crime fanatic and someone who happens to study the link between brain and behaviour, I’m going to attempt to provide brief answers to those questions (except for that last one, only time will tell – sorry).
First things first, a traumatic brain injury (let’s call it TBI from now on) is an insult to the brain that is caused by external, mechanical forces. They do not always affect the same brain regions, and some of them are quite severe while others are rather mild. Hence, they do lead to a wide range of consequences, varying in both duration and severity. Amongst those, personality changes can happen, and while they are mild (or subclinical) in some people, they can lead to criminal behaviors in others. Here comes the answer to “Why is that?”: TBIs can affect the frontal area of the brain (the region right behind your forehead and eyes) and other regions involved in frontal networks. All brain areas are important and serve certain functions (we do not only use 10% of our brain, I’m not going to talk about it today but Google it). Well, the frontal lobe is involved into a set of cognitive processes (called “executive functions”) that serve as the management system of the brain. These are the functions that enable us to reach goals and respond to complex demands from our environment. Alterations to frontal areas of the brain can lead to abnormalities in these functions, such as decreased inhibition, or “self-control”, and changes in moral decision-making. Now, in some people, a lack of inhibition could simply mean being a bit more impulsive than your peers (think about that kid who never raised his hand to speak in class). However, in others, a lack of self-control can lead to increased aggressive behaviour. This could be why TBI and criminal behaviours co-occur in some people. On that note, neurological studies do show that frontal lobe damage is more frequent amongst criminals, compared to the general population. Similarly, criminal behaviours are more frequent in people with this type of brain damage, compared to alterations in other brain areas.
Now, do all TBIs lead to violence and criminal offences? No. Despite there being an increase in criminal behaviours in people with TBI, it only happens in about 9% of them. For those who didn’t do the math, that means that over 90% of people with TBI will never commit a crime. Furthermore, past TBI is not the leading risk factor for criminal behaviour. On that note, some researchers have suggested that the coexistence of crime and head injury could be explained by a greater incidence of TBI in people who are already at risk of committing crimes. For instance, Edmund Kemper had already murdered his grandparents when he suffered from a brain injury. In that context, the relationship between these two factors could be that people who already display risky and problematic behaviours may be more at risk of incidents, in general, than others. Moreover, people who come from disadvantageous background, who are sadly more at risk for criminal behaviours, may be more likely to suffer from a TBI. Both John Wayne Gacy and Ed Gein had head injuries as a result of parental violence, which is an even more common factor amongst serial killers than TBIs. Nevertheless, when compared to unaffected siblings, people with TBI tend to show more criminal behaviours, suggesting there is a temporal link between brain injury and criminal behaviours.
In conclusion, head injuries could lead to personality changes if the brain is affected. Still, these changes are subclinical in many people, and do not necessarily lead to criminal behaviour, even less serial killing (there needs to be way more ingredients in that cocktail). On a lighter note, there is scientific evidence that psychological and cognitive symptoms resulting from a TBI could be alleviated by cognitive and behavioural rehabilitation (hooray for therapy!). So, if anything happens to your head, go to your local specialist to be sure that everything is fine and stays fine, take good care of yourself, and do not worry about becoming a murderer.
I hope I am leaving you with a better understanding of the link between head injuries and criminal behaviour. I want to acknowledge the work of researchers, who wrote scientific material on the subject. I vastly recommend the papers I used to write this (referenced below) if you wish to get a better grasp on the subject.
Brower, M. C., & Price, B. H. (2001). Neuropsychiatry of frontal lobe dysfunction in violent and criminal behaviour: a critical review. Journal of Neurology, Neurosurgery & Psychiatry, 71(6), 720-726.
Buchanan-Dunne, M.J. (October 2017). Serial Killers / Murderers and their Head Injuries as a Child. Retrieved from https://www.murdermiletours.com/blog/serial-killers-murderers-and-their-head-injuries-as-a-child.
Darby, R. R., Horn, A., Cushman, F., & Fox, M. D. (2018). Lesion network localization of criminal behaviour. Proceedings of the National Academy of Sciences, 115(3), 601-606.
Fazel, S., Lichtenstein, P., Grann, M., & Långström, N. (2011). Risk of violent crime in individuals with epilepsy and traumatic brain injury: a 35-year Swedish population study. PLoS medicine, 8(12), e1001150.
Gordon, W. A., Zafonte, R., Cicerone, K., Cantor, J., Brown, M., Lombard, L., … & Chandna, T. (2006). Traumatic brain injury rehabilitation: state of the science. American Journal of Physical Medicine & Rehabilitation, 85(4), 343-382.
Gurley, J. R., & Marcus, D. K. (2008). The effects of neuroimaging and brain injury on insanity defenses. Behavioral sciences & the law, 26(1), 85-97.
Laborde, A. (2000). NIH consensus development panel on rehabilitation of persons with traumatic brain injury. The Journal of Head Trauma Rehabilitation, 15(1), 761-763.
Leon-Carrion, J., & Ramos, F. J. C. (2003). Blows to the head during development can predispose to violent criminal behaviour: rehabilitation of consequences of head injury is a measure for crime prevention. Brain injury, 17(3), 207-216.
McKinlay, A., Corrigan, J., Horwood, L. J., & Fergusson, D. M. (2014). Substance abuse and criminal activities following traumatic brain injury in childhood, adolescence, and early adulthood. The Journal of head trauma rehabilitation, 29(6), 498-506.
Sarapata, M., Herrmann, D., Johnson, T., Aycock, R. (1998). The role of head injury in cognitive functioning, emotional adjustment and criminal behaviour. Brain Injury, 12(10), 821-842.
Slaughter, B., Fann, J. R., & Ehde, D. (2003). Traumatic brain injury in a county jail population: prevalence, neuropsychological functioning and psychiatric disorders. Brain Injury, 17(9), 731-741.
Turkstra, L., Jones, D., & Toler, H. L. (2003). Brain injury and violent crime. Brain Injury, 17(1), 39-47.