Can a traumatic brain injury explain a killing spree?

From Nature:

Why a U.S. Army soldier suspected of killing 16 civilians in Afghanistan did what he did is still unclear, but one thing is certain: his lawyers are likely to invoke emerging science about the effects of war on the brain to aid in his defense. In fact, even before Staff Sgt. Robert Bales' identity was revealed, unnamed US officials were telling major news outlets that the suspect had suffered a traumatic brain injury, or TBI. Shortly thereafter, Bales’ lawyer publicly suggested that his client suffered from Post-Traumatic Stress Disorder (PTSD), even though it does not appear to have been previously diagnosed.

How much either TBI or PTSD could explain a pre-planned rampage is up for debate, however. According to Dr. James Giordano, director of the Center for Neurotechnology Studies at the Potomac Institute for Policy Studies in Arlington, Virginia, TBI manifests itself through a variety of complaints, which may range from mild to moderate. These could include disorientation, ringing in the ears, vertigo, and headaches, as well as a more profound constellation of severe neurological and psychological symptoms, such as impaired impulse control, acting out and aggressive behavior. “What we're seeing is that TBI presents as spectrum disorder with a variety of effects,” says Giordano. In fact, some people make a complete recovery from TBI, while others develop more severe conditions down the road, and it’s difficult to predict which injuries will persist, according to Giordano. “One would think the milder the injury, the less severe the symptoms,” says Giordano. “That’s not always the case.” The Pentagon estimates that over 230,000 troops have suffered some form of TBI over the past 10 years.

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