For the defense: TBI does lead to criminality
In one study by Brooks et al of 42 individuals with severe TBI, threats of violence increased from 15% 1 year after sustaining head injury to 54% 5 years after.4 Whats more, at the 5-year follow-up, 31% of these patients had legal problems and 20% of their relatives had been assaulted by them at least once.
A study by Sarpata et al also supports the argument that TBI leads to criminality.5 They argue that TBI patients should be expected to commit crimes because they have poor cognitive skills, impulsivity, and increased aggression, as well as low tolerance for frustration and poor judgment. In their study of 18 subjects in a community corrections day program in Vigo County, Indiana, they found that a large percentage of offenders (50%) reported head injury.5 In contrast, the prevalence of head injury in the general population is 2%to 5%.