Can traumatic brain injury (TBI) lead to criminal behavior?

After light heavyweight champion Jon Jones was arrested for a hit-and-run incident in New Mexico, UFC color commentator Joe Rogan speculated that brain damage from his mixed martial arts career could have contributed to his decision to allegedly flee the scene of the crime.

“If the brain is getting damaged and if we have proven that some of the issues with people that have brain damage is impulse control, you’ve got to wonder when you see fighters do wild, crazy [expletive], how much of that is due to getting bonked in the [expletive] head all the time?” Rogan remarked.

His theory appears to be correct — at least, in general. Research suggests there is a modest causal association between TBI and the risk of being convicted of a crime.

TBI occurs when a sudden hit or blow to the head damages internal brain tissue, which can cause and worsen a wide range of psychiatric symptoms. The damage appears to disrupt the function of the brain’s waste removal system. Research has found that repeated mild injuries — such as punches to the head — can have the same impact as a single severe blow.

Previous studies have found a link between TBI and criminality, and a new study published in PLOS One strengthens those findings by accounting for variables that were not controlled for in earlier research.

“With increasing concerns expressed about TBI among soldiers returning from conflicts such as Afghanistan and in those engaged in body contact sports a rigorous examination of the purported link between TBI and criminality is relevant, timely and important,” the researchers wrote.

The study was based on data from 7,694 individuals who sustained a TBI resulting in a hospital admission, 22,905 unaffected community controls and 2,397 sibling controls. The researchers found that TBI increased the risk of being convicted of a crime by two folds.

Of course, that doesn’t mean everyone who suffers a TBI will become a criminal, or that criminal actions are excused because of TBI.

The researchers said the link between TBI and criminality appears to be a result of increases in aggression or impulsivity caused by TBI. This explanation is supported by another study, which found drivers who had experienced TBI reported significantly higher incidents of serious driving aggression.

“In conclusion, the results from the current study would be consistent with a causal relationship between TBI and subsequent criminal convictions, and convictions for violence in particular, in both sexes. Successful reduction in the prevalence of TBI, a major public health imperative, could also have benefits in terms of crime rate reduction,” the researchers wrote.