You would be fully justified to state that traumatic brain injury (TBI) can cause and worsen a wide range of psychiatric symptoms including psychosis, mood symptoms, anxiety, cognitive deficits, and impulsivity. Could you also present sufficient evidence of TBI as a cause of violence?
That could be more difficult. TBI-induced criminality remains a central and controversial area within forensic psychiatry. Behavior resulting from injury has been implicated in violence and crime, especially when coexisting with substance abuse, a violent environment during childhood including abuse, and pre-existing personality disorder. The literature is vast and covers a spectrum of opinions, allowing the forensic psychiatrist to find evidence that would support the prosecution or the defense. Judge for yourself.
For the prosecution: TBI is no defense
In his study, “Brain injury and criminality,” Virkkunen concluded that “sociopathy, alcoholism, and drug abuse are the types of psychiatric disorders associated with criminal behavior, not organic brain syndrome.”1
This statement was based upon a retrospective analysis of World War II veterans. A search was conducted through Finland’s Criminal Register to compare the frequencies of convictions for crimes punishable by imprisonment between a non-TBI control group and a TBI group. The overall crime rates between the two groups were not significantly different: 5.5% versus 4.2% for the control and TBI groups, respectively. Seventeen of 1,870 (0.9%) of the TBI patients committed violent crimes versus 3 of 500 (0.6%) of the control group. A closer examination revealed that most convictions were associated with alcohol in both groups.
Unlike Virkkunen, Kreutzer et al were unable to prove or disprove a cause and effect between TBI and violence. In their 1991 investigation based on 74 TBI patients, they found that 20% had been arrested pre-injury, and 10% had been arrested after the injury.2 Most arrests occurred after use of alcohol or other drugs. The study concluded that criminal behavior might be a result of post-injury changes including poor judgment, apathy, and other new behaviors.
There are several coexisting theories. The vulnerable amygdala, located within the anterior temporal lobe, is often injured. The amygdala adjoins emotions to thoughts. Damage to the amygdala has led to poor impulse control and violent behavior. In addition, frontal lobe lesions frequently result from damage caused by bony upward projections from the skull. “Orbital frontal lesions resulting from contusions of neural tissue against the floor of the anterior cranial vault can occur when an individual falls backwards striking the occiput against a firm surface.”10 This damage impairs the TBI patient’s ability to regulate limbic input. Therefore, the disinhibited TBI patient with frontal lobe damage often reacts impulsively and even violently.
Damage to specific neurotransmitter systems also causes impulse dyscontrol in TBI patients. The locus ceruleus in the forebrain is often injured, leading to elevations in norepinephrine in post-TBI patients. Increased norepinephrine levels have been correlated with aggressiveness and impulsivity. In addition, studies by Porta et al12 and Hamill et al13 showed that dopamine was increased in post-TBI patients. Agitation and aggression have been proven to result from hyperdopaminergic states. In contrast to dopamine and norepinephrine, reduced serotonin levels (CSF 5-HIAA) lead to increased impulsivity and aggression. Although the results have varied, studies have shown changes in serotonin levels after TBI.10 Hence, much evidence supports the biological basis for impulsivity in TBI patients.
Substance abuse, traumatic brain injury, and crime were indeed interconnected, the researchers said, but they did not go so far as to conclude that TBI causes criminality and violence. Rather, they believed that substance abuse, which was most common among those younger than 35, led to legal difficulties and TBI.
In 1995, based on a larger sample of 327 patients, Kreutzer and associates found that the TBI criminal population has a relatively high incidence of alcohol abuse before and after head injury.3 Most crimes were associated with substance abuse, such as drug possession or driving under the influence of alcohol.
The study found that TBI patients with a history of arrest were more likely to have substance abuse problems after the injury. TBI patients with both a criminal and substance abuse history also were more likely to commit crimes after the head injury. Kreutzer concluded that TBI is not a risk factor for crime without such a history.
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 What’s 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.