What's the link between PTSD, TBI and violence?

What's the link between PTSD, TBI and violence?
By Dr. Charles Raison, Special to CNN
updated 8:53 AM EDT, Thu March 22, 2012

STORY HIGHLIGHTS
A lawyer for Sgt. Robert Bales says the soldier may have been suffering from TBI, PTSD
Sometimes our understanding of psychiatry is unsatisfying, Dr. Charles Raison says
Raison: The backstory to someone's life is just as important as the current situation

Editor's note: Dr. Charles Raison, CNNhealth's mental health expert, is an associate professor of psychiatry at the University of Arizona in Tucson. He has not personally examined the suspect in the Afghanistan mass shootings, Robert Bales, but has used news accounts as the basis for his views.

(CNN) -- Q: Sgt. Robert Bales has been accused of killing 16 Afghan civilians. He served three tours in Iraq before this and his lawyer says he may have been suffering from post-traumatic stress disorder or a traumatic brain injury. What's the link between violence and those disorders?
A: Psychiatrists understand some types of aberrant behavior pretty well and can do things to help resolve it. But, unfortunately, in other instances -- and often the most interesting ones -- we can only mumble generalities that require no special expertise and that offer no hope for a diagnosis or treatment.
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