Even a mild concussion can cause disconcerting and sometimes lasting symptoms, such as trouble concentrating and dizziness. But can it make someone more likely to commit a crime? After all, a disproportionate number of people in the criminal justice system previously suffered a traumatic brain injury (TBI). But according to new research into the medical and juvenile justice records of Danish teenagers who suffered a blow to head as children, such injuries don’t cause criminal behavior. Although TBI and criminality often travel together, the researchers found in this Danish population it’s a case of correlation, not causation.
“I think this study very clearly indicates that you can’t just [say], ‘Hey, my kid has a mild TBI, he or she is screwed,” says Joseph Schwartz, a criminologist at Florida State University who has studied the issue in juveniles and adults. At the same time, he cautions that there are important variables this study wasn’t designed to capture, such as the treatment received, the effect of repeat TBIs, and the circumstances surrounding the injury. All of these, he says, could influence criminal behavior in some people.
Beyond showing high rates of past TBI among those charged with or convicted of crimes, research into this topic has been limited. Studies have found that mild TBI is associated with later behavioral problems, including impulsivity and inattentiveness, which are also linked with criminal behavior. At the same time, it’s well known that “the risk factors in the child and the family for TBIs are the same as the risk factors for delinquency,” including poverty and parental substance abuse, says Sheilagh Hodgins, a clinical psychologist at the University of Montreal. She notes, too, that impulsivity and attention and conduct disorders heighten the risk of sustaining a mild TBI in the first place.
To look more closely at the relationship, a team of Danish sociologists took a big-picture view, mining their country’s databases for medical records from children born between 1995 and 2000 and identifying those diagnosed with a mild TBI (also called a concussion) in elementary school. That worked out to about 4% of all children, or more than 13,000 youngsters. “It’s not that rare” to have a concussion at this age, says study co-leader Ea Hoppe Blaabaek, a sociologist at the University of Copenhagen and the ROCKWOOL Foundation, which studies health inequalities. (Her own son suffered a concussion at age 5 when he was hit in the head with a rock.)
Then, the group examined how many of those 13,000 had contact with the criminal justice system between ages 15 and 20. They used as a comparison group 329,000 children born in the same time range who didn’t have a mild TBI in their medical records. Kids who’d suffered a concussion were more likely to face criminal charges or convictions: 8.4% who’d had a mild TBI were charged with a crime as teens, and 6.6% were convicted, versus 6.3% and 5%, respectively, in the comparison group. “That’s quite a large difference,” nearly a 30% increase, Blaabaek notes. The pattern held even when researchers broke out crimes by type—assault or vandalism, for example—or by the offender’s sex.
Then came the big question: Did the concussions predispose youths to committing later crimes? To tease this out, Blaabaek and her colleagues examined whether mild TBIs were linked to criminality among kids who were otherwise similar, particularly siblings growing up in the same family. They also controlled for parents’ education, birth weight, and other factors. With those controls in place, the association between concussions and later contact with the criminal justice system disappeared, the team reported yesterday in JAMA Pediatrics.
There are various explanations for the effect on crime disappearing, the authors and outside researchers agree. Blaabaek notes that “crime is a fairly extreme outcome,” and a mild concussion may rarely damage the brain enough to drive such behavior. (She stresses that the study can’t say whether a severe TBI leads to criminal actions.) It’s also possible that younger children can more easily recover from mild brain injuries.
One limitation of the work, Blaabaek and outside researchers note, is that parents who take their child to the hospital following a head injury may be different from parents who don’t, including those who aren’t aware an injury occurred because their children lack supervision. It’s possible that the effects of any undiagnosed TBIs in the comparison group skewed the data, the authors acknowledge.
The study also doesn’t rule out the possibility that TBIs could enhance some risk factors known to fuel criminal behavior, such as impulsivity and other behavioral disorders, or growing up in a deprived home, Hodgins says. “The problem is that the risk factors … are there from very early on in life, and we don’t know when the initial TBI occurs,” or how it might intersect with those factors.
It’s a tough question to study. In a paper published in July in Frontiers in Neuroscience, Hodgins and colleagues reported that among children who sustained a mild TBI, only those who also had disruptive behavior disorders showed changes in white matter in several brain regions—suggesting these risk factors may build on each other in ways that aren’t well understood.
A brain injury may also have knock-on effects that can be tough to untangle, Schwartz says. In a multiyear survey of youth, he found that a mild TBI reduced impulse control, which in turn can lead to criminal behavior in some.
And the circumstances of the injury may matter, too, Schwartz says: A child who sustains a mild TBI from falling off a bike may experience different behavioral changes from one who’s injured by abuse and suffers from exacerbating psychological trauma.
Although the Danish study is instructive on a population level, it still doesn’t resolve the burning question: “Do [TBIs] enhance these risk factors that are already there, or not?” Hodgins says. Answering that might even reveal ways to reduce a childhood concussion’s aftereffects and help kids build resilience.
