Historically, there has been an association of violent crime and traumatic brain injury (TBI). There are numerous case studies of violent behaviors after TBI, and there is an extremely high prevalence of prisoners with TBI. This association is in part due to the vulnerability of the frontal lobe to injury-the frontal lobe is critical for emotional control and inhibition of inappropriate responses and behaviors (among other things). However, there is little research that supports the causal relationship of TBI and violent crime. Other factors such as substance abuse, impulsivity as an inherited trait, and socio-economic status can also contribute to violent crime.
Researchers recently found that, after controlling for these confounding factors, there was still a direct association between violent crime and TBI. In addition, injuries to the frontal lobe were significantly more likely to be associated with violent crime than other areas of injury. Despite the fact that substance abuse and impulsivity can increase the risk of TBI, the study found that a frontal lobe injury can independently increase violent behavior.
Faxel S, Lichtenstein P, Grann M, & Langstrom Niklas. Risk of violent crime in individuals with epilepsy and traumatic brain injury: A 35-year Swedish population study. PLOS Medicine. (December 2011).