The Truth about Traumatic Brain Injuries and Violent Behavior

You may have seen headlines about traumatic brain injuries and violent behavior, but now it’s time to delve into the truth. We’ve put together a few facts that you may not know. Let’s start with a few basics.

What is a traumatic brain injury? When the medical world talks about traumatic brain injury (TBI for short), they mean harm or damage to the brain that does not degenerate over time and was not present at birth (non-congenital). The harm results from an outside mechanical force that strikes the brain and results in permanent or temporary disability with respect to the person’s cognitive, physical and psycho-social capabilities, often accompanied by diminished or altered consciousness.

The definition has not enjoyed a consistent use and often varies by circumstances and by medical specialty. We often hear it as a synonym for head trauma and not always with neurological effect.

How do experts define violent behavior? Therapists define violent behavior as the use of physical force to injure another person or destroy property.

Is there biological evidence of TBI causing violence? Yes. For example, the amygdala resides in the frontal lobe. The amygdala joins a person’s emotions to his thoughts. Therefore, if the amygdala sustains injury through the TBI, then the patient exhibits poor impulse control and violent behavior. If the temporal lobe has lesions caused by damage from pieces of skull bone piercing the temporal lobe, then the patient has difficulty regulating limbic input. The limbic system is an area of the brain made up of nerves and neural networks that relates to instinct and mood. Injury to this system can result in impulsive and violent behavior.

In addition, damage to neurotransmitters can result in an increase in the chemical norepinephrine which can cause loss of impulse control in TBI patients. Other studies showed increased dopamine in TBI patients which leads to aggression and agitation. Still other studies have shown a reduction in serotonin levels in TBI patients which leads to increased impulsive and aggressive behavior.

How does medical evidence of TBI work in the courtroom?

Stephen J. Morse, professor of law and psychology at the University of Pennsylvania is also a member of the MacArthur Foundation Research Network on Law and Neuroscience, a group that studies in the area where neuroscience meets criminology. He says that neuroscience has added nothing to the study of law because people commit crimes, not brains. It’s not that he disagrees that brain injury can cause lapses in judgment or loosen inhibitions. It’s that the studies so far cannot show whether or how the person tried to control his impulses and whether other factors besides the injury contributed to his impulses.

Still, lawyers bring TBI defenses more often into the courtroom each year. Many of these cases center around neuroscientific evidence with respect to defendants who served in combat in Afghanistan and Iraq. In addition, there are now special veterans’ courts, 80 in total. These courts began in recognition that veterans have special health issues related to their service in combat. The veterans’ courts emphasize rehabilitation over prison time.

TBI’s effect on the criminal justice system is not going away any time soon. Experts expect more criminal defendants (not just veterans with TBI) to bring in medical evidence of brain injuries to explain or mitigate their criminal behavior.

One indication that this line of defense will continue to move into courtrooms, the University of Wisconsin and Vanderbilt are among universities now offering a degree program in neuroscience and the law.

To read how TBI may have played a role in the Aaron Hernandez criminal case (as well as his suicide), read the article entitled “Suicide, Violence, and Chronic Traumatic Encephalopathy: The Fight Over Aaron Hernandez’s Brain.”

To talk more about this topic, or anything else, please contact us. We are your resource for criminal law issues.