Sustaining a traumatic brain injury (TBI) may be a risk factor for violent behavior and subsequent incarceration, new research suggests.

A large review of birth cohort, data linkage, and population studies showed mixed results individually. But overall, there appears to be a significant association between TBI and increased risk for violence, arrests, and an earlier age at time of conviction.

One birth cohort study from Finland, which included 12,000 male participants, showed a fourfold increased risk for a mental disorder plus offending in adulthood in those who had a TBI during childhood or adolescence. And an association with earlier onset of criminality was found when a TBI occurred before the age of 12. However, no adjustments were made for confounders.

A study conducted in England showed that those who had experienced mild TBI were at significant risk for criminal behavior, although these associations were confounded by substance use.     

Among the data linkage studies, a 35-year retrospective analysis in Sweden showed a "substantially increased risk of violent crime" in those who had an earlier TBI, as did a study from Australia that used a sibling control group, as well as a recent study of 1.4 million individuals in Ontario, Canada, even after controlling for potential confounders.

"TBI might be, at the very least, a prominent marker for a range of issues that indicate a risk for crime," write the researchers.

Lead investigator W. Huw Williams, PhD, Department of Psychology, University of Exeter, United Kingdom, told Medscape Medical News that the main finding "we drew out was an increase of crime after a TBI by a factor of about 2."

This wasn't a meta-analysis, but there seems to be a doubling of risk for crime when there's a brain injury present, although that risk could be lessened depending on various criminogenic factors that are present in the person's life," said Williams.

"Also, we found that the rates of brain injury in young people and adults in prisons was about 3 to 5 times higher than you'd expect in the general population."

The review was published online February 26 in the Lancet Psychiatry.

Comprehensive Review

"TBI is the largest cause of mortality and morbidity in children and young people," write the investigators. They note that lifetime prevalence of a TBI is about 8% to 12% in the general population.

"There have also been a number of studies emerging indicating a link between brain injury occurring and then later crime. But that hadn't been put together [before] comprehensively," said Williams.

Among the three birth cohort studies included in the review was the study mentioned earlier from southwest England. It included 800 participants with a history of mild TBI and 8307 without a history of TBI.

Results showed that the former group was at a significantly greater risk for criminal behavior by the age of 17 than the latter group (unadjusted odds ratio [OR], 1.6; 95% confidence interval [CI], 1.2 - 2.2), but substance use was a confounder.

Interestingly, the TBI group's risk for criminal behavior was almost identical to that of another group that comprised about 2300 participants who had had an orthopedic injury (adjusted OR, 1.1; 95% CI, 1.1 - 1.6).

"However, TBI was linked to hazardous alcohol use, externalizing symptoms, conduct problems, and ADHD [attention-deficit/hyperactivity disorder]," write the investigators.

Another birth cohort study followed 1265 children in New Zealand until they reached the age of 25. Those who had had a TBI were significantly more likely to be arrested than those who had not. However, the association was no longer significant for those who received their injury before the age of 5 after controlling for later alcohol and drug dependence.

"Early substance use could be a mediating factor for crime in those injured at a very young age," the researchers write. They note that evidence from birth cohort studies that TBI leads to crime is "mixed."

Independent Risk Factor

Among the four data linkage studies included in the review was one conducted in northern Finland. It showed that, compared with those who had not had a TBI, those who had experienced a TBI were at 6.8 times' greater risk for any criminality. They also had committed more violent crimes (42.9% vs 9.1%, respectively) and nonviolent crimes (29.4% vs 6.8%).

In the Swedish study, violent crimes were committed by 8.8% of 22,914 individuals who had had a TBI vs 2.3% of the general population control group, yielding an adjusted OR of 3.3. The OR dropped to 2.0 when the TBI group was compared with their unaffected siblings.

Compared with a control group of nearly 23,000 participants in Western Australia, patients who had had a TBI (n = 7694) were at increased risk for criminal activity as a whole for both men (hazard ratio [HR], 1.6) and women (HR, 1.5).

After controlling for same-sex full siblings, the risk remained significant only in the male participants who had had a TBI (HR, 1.7).

Both men and women who had had a TBI were also more likely than the control group to have convictions for violent behavior (HR, 1.7 for both sexes). Only the men with a history of TBI were at increased risk for violent offending compared with their full siblings (HR, 1.9).

TBI was also significantly associated with an increased risk for incarceration among 1.4 million adults in Ontario, Canada (HR, 2.5).

Overall, "considering the range of evidence, across age groups, populations, and jurisdictions, these studies indicate that TBI is an independent risk factor for crime," write the investigators.

However, "there is a lack of clarity on actual causal mechanisms," they add. "It might be supposed that having a TBI would typically lead to — or exacerbate — problems in behavioral self-regulation and mood [but] higher research is needed."

High Prevalence Rates

In additional literature review, the researchers found that in one meta-analysis of nine studies, 30% of juvenile offenders had a history of TBI, at an OR of 3.37, vs a control group. Other studies showed that "adversity and comorbid issues" are also very common.

"Young offenders with TBI are particularly at risk of self-harm and suicidal behavior," report the investigators.

Another meta-analysis, which included 24 studies and 5049 incarcerated adults, showed a pooled prevalence of 51% for TBI.

The new review also showed significant associations between TBI and reconvictions, infractions while in custody, and not fully engaging in treatment.

"Prison systems need to take brain injury into account when they're trying to rehabilitate people who offend," said Williams.

As for clinicians, he noted that it's important to try to ascertain whether a complicated mild or moderate to severe brain injury could contribute to a patient's symptoms of depression, psychosis, or posttraumatic stress disorder.

"Taking into account some of those issues might better help people to change their behavior, especially in the adolescent and young adult period," he said.

Although TBIs are often regarded as coincidental occurrences in the lives of risk takers, Williams noted that that might not be true.

"When a brain injury happens, it typically affects the frontal lobes, which are responsible for controlling impulses and for behaving appropriately with other people," he said. An individual "may well be part of this risk taking, but I suspect that the brain injury exacerbates or amplifies these tendencies, which leads to greater crime over time."

Inconclusive Findings?

Asked to comment, however, Donald G. Stein, PhD, director of the Emergency Medicine Brain Research Laboratory at the Emory University School of Medicine, Atlanta, Georgia, told Medscape Medical News that he has several concerns with the review and is skeptical about the findings.

Dr Donald Stein

"There are so many qualifications throughout the article, so many variables that can influence a TBI, that I personally think it's inconclusive," said Stein. "It's certainly not a definitive article in terms of showing that TBI causes violent crime."

Asked if he thought the review at least showed that a link between the two may be possible, Stein said, "Yes, but you can make that case for anything."

He added that previous research suggests that certain types of brain injuries can lead to a lack of impulse control and of executive judgment and might influence risk-taking behavior. "But does it absolutely ensure that you're going to commit a crime? They didn't even really define what a crime is," he said.

Stein also pointed out that some individuals with a TBI might worry that this study is saying that they could become criminals, and that others might look at this as a way to help in their defense of criminal behavior.

"Does this mean a person with a TBI is no longer responsible? Will they try to say, 'I'm a victim of my TBI'? There are a lot of factors that you have to be careful about in making sweeping generalizations until you're really certain of the facts," he said.

Dr Williams has received grants from the Barrow Cadbury Trust and is a vice chair of the Criminal Justice and Acquired Brain Injury Group. Dr Stein has reported no relevant financial relationships.